what would cause

[K5Greek]

and engine to rev high by itself? also when its reving high the truck downshifts late. like if im slowing down at a stop sign itll downshift at around 5mph...as soon as i turn it off then back up its gone, but this is like the third time its happend to me now. i can tell its reving high too becuase when i pull out of driveway, i dont need to give it any throttle and itll go and shift into 2nd

 

[southernspeed]

Something fouling the throttle linkage. Dirt in the TB causing the butterfly to hang open. Sticking throttle cable. really bad air leak.
Just a few ideas.

 

[vortec]

i'd start by looking for vacuum leaks.