What should I do? 2015 Volvo VNL 780

I would just run your own setup. I just got out of a Volvo but I had a dual setup and worked great. I just left the stock stuff alone and bought everything I needed to mount my setup.

 

I was running dual 6ft firestik antennas with the 18ft fire-flex coax and mounting on top of the mirror with those mirror mounts. My radio is a Cobra29 w/ blue tooth that's been tuned and I can get some really good range out of it.

 

Bird perch works fine. I found that the big 1-1/4" mirror mount that Roadpro sells works well, if you take a piece of braid and run it from the mount to one of the mirror screws (into the door).

Don't bother with running dual antennas. While you can (theoretically) get some gain from them, it's not worth the headache of tuning two antennas. If you like the look, just mount the second one and don't connect it to anything; consider it a spare.

I'm surprised that the stock setup isn't working for you. I get a couple of miles easily on my stock 670 with an untouched (legal!) CB.

 

I'm running a older Phillipines 148GTL on the original single antenna, with the shroud with no problems, and can hear and get out fine.

 

use the "bird perch" and your choice of antenna with your own coax. i have driven volvos for years and this is the best setup out there for them. no issues at all running any radio. amps can be run too, but they need to be run direct to the batteries for best performance. any radio should be run right off the batteries, but sometimes you cant do that on company owned trucks.