1998 Cheyenne Trans Problem

[swampeep]

Transmission seems to shift through 1st & 2nd gear at very low speeds, then as it shifts to 3rd gear the engine loses rpms and starts bucking. If I let off the gas,  the engine recovers and eventually goes on normally. I have been shifting manually to avoid the problem, this works but still shifting hard into 3rd gear. Had the truck in the shop, no codes and they were unable to recreate the problem. Was an intermittent problem but now does it all the time.

[DL_98 Sierra]

Bad ground, torque converter or sensor???