Wire is not a good ground for RF signals. RF travels across the outside of the conductors, known as "skin effect". A braided ground strap is better.
Did you grind your grounding points down to bare metal before screwing-on the contacts? This will further affect the ground.
Do you have a safari rack or tire swing with a rack, jerry cans, etc? Make sure these items are also strapped to ground as they can cause reflections.
Is there a lot of extra coax coiled up in a loop? This will act as an inductor and will affect SWR.
Did you check your connectors to see if there's any loose strands of braid that might be contacting the center conductor?
Did you install the plastic isolator (washer) on the bottom of the antenna before you screwed it into the mount? Did you perhaps over-tighten the antenna/connector and compress the isolator? The antenna must not make electrical contact with the mount (or any other part of the vehicle). Also check that the connector on the bottom of the mount to make sure it is mounted straight and centered. The isolator should have a shoulder that sticks into the mounting hole to do this, but if things aren't straight it could be a problem.
You could have a bad piece of coax. I've seen it happen. You can't measure impedance with an ohmmeter or via DC voltage drop, it is frequency-dependent. And SWR isn't really related to impedance, but rather mismatches in impedance, which includes metallic objects in close proximity. Try another piece of coax. Run it outside the Jeep to test it first before committing to installation.
Although less likely, it is possible you have a bad antenna or radio. I've never had or seen a Firestick be bad or go bad that didn't show very obvious signs of damage, but that's no guarantee. I've also never seen a radio be bad in regards to SWR, but technically this is also possible.
Wow, that is a great response. I was starting to wonder if anyone was going to answer. I'll try to respond to your questions one at a time.
Braided strap: OK,,, I didn't use a braided strap. I had read that 10 or 12 ga wire works just fine, so I took the easy route. Obviously some people have had success this way. Something that I will see about changing. It may be easier to find a new place to mount my antenna.
Grind away Powder Coat. Yes I did. In fact, I went back and did it more, and I did get better results with my multimeter. So, there was a problem, but I really don't think it is an issue now.
No Safari Rack or Gas CanHolder. Other than a windshield light bar, no add ons.
Extra coax: No extra. By the time I ran in and out of my tail gate and up the passenger side and across to the bottom of the drivers seat, I only had about a foot left. I was surprised, but that isn't an issue.
Loose Braids: I bought an 18' piece of coax from a truck stop with factory ends. They are sealed. I assume that they are OK.
Mounting Stud: Yep, the plastic washer is in place and snug, not crushed. I even checked with my multimeter to see if the top of the stud was grounded. It is not. That appears to be just fine.
Bad Coax: Well, I have no way of knowing unless I buy another piece. I just moved to SoCal and I don't know anyone to see if I can borrow a piece. I'll toss a post on the California Members section and see if someone will loan me a section of coax for 3 minutes. I don't have a problem buying new coax, I just hate to start replacing parts that don't need to be replaced. It would be great if that was the problem and the fix was that easy.
Bad Antenna: That would suck. My Firestik is brand new and I have no way of knowing if it is good or not, and no way of testing. This will be my last piece to look at.
Thanks for all of your help. I'm not really sure where to start. I feel like I've done everything. Changing the ground strap seems iffy. With so many people not having issues that did it the same way seems like it wouldn't make that much of a difference.
I think I'll grab a hunk o metal and do a mount off of my hood to see if that changes things.
I'm spinning right now because this has caused more problems than it should have.