This truck is new 2500 HD factoy preped for snow plow, here is my problem, charging system alows bat. to go down to 9v. then kicks Alt in and takes it up to 14-15 volts when this take place
(only when Im plowing)
I here belt slip and some times I can even smell a faint smell of rubber
I have taken this problem back to dealer they could not duplicate problem, just wondering if I should try to put a small pully on Alt.
Belt tentioner is good, the Alt is quit a bit oversize part of the prep package.

 

I was in the shop the other day and heard a tech telling one of the service writers that there was a "new Belt tensioner" that the truck needed. He had a very similar problem to yours. From what I gather it depends on the production date of the vehicle if yours has the new or the old style tensioner on it. I would give the dealer a call and ask them about it anyway. That may be the whole cause to the slippage problem your having.
Good luck to you.