Is Pepper's a radio shop? If so, then get him to bench test it so you know what's going on. There's a good shop in Carlise, but thats a long ways from you. TG for the internet, now you can just Google and find reviews/info on just about anything (at least that's what i do). All manufacturers produce different grades of radios, so YES, Galaxy has some awesome radios (in the Hundreds of $$ range), but I couldn't tell ya which models. Like Ron, I too prefer Cobra's and they've been around for a LONG time (Ken, a friend who got me into CB's, had this awesome Cobra AM/SSB Base Station and we use to talk CQ-DX on the weekends in the early '70's) but I digress...
I agree that is sounds like it might be a broken/loose Mic, or Mic plug, wire. Have you had ur SWR's checked? How about ur Coax connections? A cheap Uniden I had died on me because I had corroded connections, not the radio's fault.
As I mentioned before, there's hundreds, if not thousands, of sites on the Net that can help ya "correctly" set up a CB in a vehicle (its not as simple as most people think).
Let us know how you make out.
Jack