2007 gmc sierra will idle but will not drive!

[justinblake1994]

My father bought is 2007 GMC sierra 2wd 4.3 new back in 2007 when the new bodystlye come out. It has 80,000 miles and rarely gets drove because he has a company vechile. He got it out and went to drive it and it started having a little miss so he added some heat and it seem to fix it. Well a month or so later he drove it again and it did the same thing and heat did not fix it. So he decided to drain the tank and put fresh gas it in and still misses. Well he was told the throttle body so he replaced it and it did not fix it. Well eventually the miss mad the tranny go out and he had it rebuilt and the guy said the tranny looked like the truck got yanked around but it never gets drove. Well it still does it. It. It will sit and idle fine till you put it in gear and it starts missing falls on its face. But you can try to power brake it and it will try to turn the tires over.
CaN not figure it out please help
Thanks Justin!