SteveShannon

The FT60r is a very nice radio for use on the 2 meter and 70 cm ham bands, but without modification cannot transmit on GMRS. GMRS is not amateur radio. 
There are some nice radios available for GMRS and they’re typically easier to use than a ham radio. 
Personally, I really enjoy being a ham and if that interests you I’d be happy to recommend study guides, but if you’re just looking for a radio to use casually with your family or friends without learning about frequencies and the speed of light, GMRS is very nice. 
Welcome to the forums and good luck whatever you want to do. 

It is the remainder of the frequency for your receiving frequency and transmission frequency:  after the "462" and "467" respectively
There are only 8 GMRS repeater frequencies, so typically they will list:
550, 575, 600, 625, 650, 675, 700 or 725

Tried on channel RPT 5 and for grins I also tried it on channel 19 (manual mentions the .650 frequency = channel 19).  No luck, no kerchunk or anything.  Maybe I'm out of reach/line of sight (only 6 miles away from the "30" mile range).  I might just drive there and test when I have the chance.  Thanks for helping and Happy Easter to you too!!  

The Comet CA-712EFC is advertised as 9 dBi. If my math is correct, 9 dBi equals 6.85 dBd.  

You bet!  Happy Easter!

You should put a quality antenna analyzer on your J Pole without the cable and sweep it and see what the antenna resonates at. Then try with the cable attached and sweep it. Then put the MXTA 26 at the end of the coax in place of the J Pole and sweep it. The results should indicate where your problem maybe located.
If you need to replace the cable "Do Not Buy Cheap Cable" from Amazon.

I live in a hollow and am surrounded on three sides.
If it is truly line of sight to the repeaters, at 20-25 miles you probably don't even need a Yagi. If you want a "One and Done" solution, then the Yagi should  be your first choice. If are also planning on eventually having a mobile unit in a vehicle, you could start with a mobile antenna on a piece of 2'x2' sheet metal just to see how good your Tx/Rx is.
If you haven't already done this, a web site such as www.heywhatsthat.com lets you map the elevation profile between you and the repeater to see just how straight a shot it is.
This image shows the terrain between my house and a nearby repeater. A 5W handheld with the stock antenna can barely hit the repeater; a 40W mobile with a 5dB Laird antenna on sheet metal on my porch is very clear. The same 5W handheld going through 70' of 1/2" hardline coax to a 5dB Laird on my roof is very clear on the repeater. (The antenna on the porch has to transmit "through" the house to get to the repeater.)

The last thing I heard about the GM-30 was that it was shipping with one channel (15) not working. I wouldn’t order one. 
I would buy a Wouxun KG-805 and watch Notarubicon videos if I were you. 

Well, this sort of nonsense is a result of a non-engaged repeater owner.  As a repeater system user, paid or not, you have no real say in what that repeater carries for traffic.  Ultimately, if you don't like it you can make a comment about it if you choose to but your final say in the matter is when you change the channel or turn off your radio.  You have NOTHING else to do when it's not your gear.  If the repeater owner allows that sort of conduct, then that's how it is. 
But an engaged repeater owner that pays attention to what's going on with his / her repeater should be dealing with that.  Telling people that they are NOT going to argue, cuss and act the fool on the repeater and to either stop or go kick rocks is the way it needs to be handled.  And if they refuse, you shut off the repeater for a while. And the repeater owner can record the traffic, get call signs if the users are actually saying them and file a complaint with the FCC.  If it's a common thing for these people to act up and break the rules (causing interference) then the FCC might get involved. 
But end users really have no say in the content.  And people shouldn't just throw up repeaters that they don't pay any attention to and let others act foolish on them.
 

I would replace that RG8 with LMR400 or equivalent. You will do a whole lot better with the correct type of coax for UHF.

The FT60r is a very nice radio for use on the 2 meter and 70 cm ham bands, but without modification cannot transmit on GMRS. GMRS is not amateur radio. 
There are some nice radios available for GMRS and they’re typically easier to use than a ham radio. 
Personally, I really enjoy being a ham and if that interests you I’d be happy to recommend study guides, but if you’re just looking for a radio to use casually with your family or friends without learning about frequencies and the speed of light, GMRS is very nice. 
Welcome to the forums and good luck whatever you want to do. 

The FT60r is a very nice radio for use on the 2 meter and 70 cm ham bands, but without modification cannot transmit on GMRS. GMRS is not amateur radio. 
There are some nice radios available for GMRS and they’re typically easier to use than a ham radio. 
Personally, I really enjoy being a ham and if that interests you I’d be happy to recommend study guides, but if you’re just looking for a radio to use casually with your family or friends without learning about frequencies and the speed of light, GMRS is very nice. 
Welcome to the forums and good luck whatever you want to do. 

The FT60r is a very nice radio for use on the 2 meter and 70 cm ham bands, but without modification cannot transmit on GMRS. GMRS is not amateur radio. 
There are some nice radios available for GMRS and they’re typically easier to use than a ham radio. 
Personally, I really enjoy being a ham and if that interests you I’d be happy to recommend study guides, but if you’re just looking for a radio to use casually with your family or friends without learning about frequencies and the speed of light, GMRS is very nice. 
Welcome to the forums and good luck whatever you want to do. 

By whom?
Yes. And some of them were not impressed:
https://forums.mygmrs.com/search/?&q=Tidradio h8&search_and_or=or
 

Sorry, thought you were talking about the N9TAX slim-jim that has a 6ft long or so pigtail. Here's a SWR plot of my KB9VBR GMRS J-Pole. Around 1.8 SWR on the low end of GMRS and around 1.3 SWR on the high end. I stopped using it awhile back, just didn't work as well as other antenna's I have.
 

Have you tried checking the SWR on the slim-jim without the additional coax? Just to rule out possible bad coax to the antenna.
Here's a SWR sweep of my N9TAX GMRS slim-jim, around 1.3 SWR on both sides of GMRS

This is the way.

Nothing wrong with getting a new radio.
I will recommend the Wouxun KG-1000G Plus over the Midland MXT500. I had both and got rid of the Midland. The KG-1000G is a better radio.

This is the way.

Speak for yourself.

Yes, and some of them are even logical.

Fixed that for you.

As Mr. @Sshannon already said, NO .

The bump in wattage will make no difference whatsoever. 
Quadrupling your power to 150 watts would only make a single point of difference on the S-meter.

I've been declared a shill and I dont even say that!