I found my mount to tailgate was well grounded, so I ran a wire from underneath the tailgate trim panel to the bolt holding the sub down. Nice and clean.

Checking with the multimeter, the ground is clean from the mount, to the tailgate, to the tub, to the frame, and even to the muffler believe it or not.

 

In all actuality you should be able to get continuity from the mount all the way to the front bumper, or ANYTHING metal that you touch with the probe....doors, tailgate, winshield frame, etc... That way the antenna is seeing one solid large metal mass as it's ground plane.

 

After running through all the tests, we found that the coax that I had installed was the issue. I installed better quality coax and it's now tuned to 1.5 on all stations.

Thanks for the help!! I appreciate it.