New Western Star 49X - SWR Too High

Just curious if anyone else that mounts an antenna on the back of the cab of the new Western Star 49X daycab is having high SWR issues. At first I thought my coax might be kinked or old, so I replaced the coax and then I quickly realized that I'm pretty sure the whole cab, bars, etc are aluminum. I have been running a Wilson 2000 with the Wilson gumdrop mount for years when we were running Freightliner Coronado daycabs. The bar on the back of the Coronado cabs where the hose connection springs mount must be metal. Because the same setup on the new Western Star 49X's...the SWR are too high for my liking. Plus I noticed my receive wasn't where it normally should be as well.

Just curious if anyone else has experienced this...and what you did to remedy it. If in fact the majority of the cab is aluminum including the grab bars, hose spring bar, etc...I'll have to figure out some sort of a grounding path as well. I slipseat, so the least amount of work, the better...but I'll do what I have to do to get my SWRs where they need to be.

For those curious of what style Western Star I'm running...please see the attached photo.

 

Too high for me was up above 2.0. When I ran the Coronado and mounted it on the back of the cab, I had it dialed in right around 1.2-1.5