Trying a new antenna

2017 Cascadia daycab with a maximum 1 mile range (I could barely hear a coworker at that distance last night).
A few weeks ago another coworker said that even within a quarter mile, I was fading in and out, sounding clear one minute, then very distant the next. He seemed to think it was my mic. I have a stock Classic 29 with an aftermarket Cobra HG M77 and factory antennas. I don't think it's the mic, but what do I know???
I just purchased a Francis antenna to see if it makes a difference. If not, maybe I'll look at a different mic..?

 

P.S. I don't want to mess around too much, since it's a company rig, and a Penske lease at that...

 

I've watched that thread before, a lot of info there, most of it over my head. That, and I don't have the time or patience to go through it again... personal downfall.
I know the gist of the thread is that the factory antenna setup is basically useless. If I install the Francis, and then add a new, better quality coax, will that make enough difference for me? I'm not looking to blast anyone, I would just like to at least get a couple more miles of range.

 

If I run a 5.5, I'll need to do a mirror bracket, we have a couple stops with very low clearance. I was hoping to stick with the original mounting points on the side of the cab, but maybe I'll have to change that.

 

Creepy...