I was almost certain places like autozone, napa, carquest carried replacement CMP's. I also thought it was a little expensive for a "guess."
Are the shops suggesting this part after looking the vehicle over, or is this simply a guess over the phone? I would normally defer my opinion to the opinion of someone who has actually ran some diagnostics. But if they haven't touched the truck themselves, then they are just guessing.
One thought: A bad CMP normally would not prevent you from pulling codes. In fact, it would trigger a code (CM 214 isn't it??). You've indicated that you were unable to pull any codes from it or even get the CEL to come on. Until someone tells me they've put a voltmeter on that red wire going into the PCM and read 12V, I'm going to stick with that as the first thing I'd do.