If the truck was able to use a single piece driveshaft, why would GM have gone to the trouble and expense to engineer a 2-piece? It sounds like you need to RUN, not walk away from that "mechanic" and find somebody who actually qualifies for the title!
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!