Slow shifting

[Meldog]

In my 94 GMC Sierra, 350 2wd, I have problems shifting/ accelerating in the 40-50 and some times 50-60 mph range. there is a lag there and even the rpms stay constant, even when i put the pedal to the floor. then after a while, it decides to accelerate and then it will go. someone asked me if it was maybe not firing on all 8. also once the truck gets warmer after i have driven it for a while, it decides to really sputter on accelerating. it shakes bad in Overdrive once it is in the 180+ range after driving it for a while.

 

any suggestions?

Thx,

Meldog