93 C2500 shifting hard

[67chevymechanic]

This is gonna sound strange, but try disconnecting the alternator and driving it. I’ve read that on the electronically controlled transmissions a bad diode in the alternator can introduce AC voltage into the electrical system and throw off the computer. Worth a shot and it won’t cost you anything.

 

[obs704]

I thought the PO installed a shift kit or something in my '93... it spins the tires on the 1-2 shift at part throttle if it's raining. But, my coffee has a lid and my other car has shifts you can barely notice, so I can live with it. -As long as it stays healthy.

BTW, same as yours, Peaches. '93, 5.7, 4L80E. Mine has 4.10 gears.

same here in my 93

 

[Sabinoerc]

I had a hard 1-2 shift in my 93 5.7 with a 4l60e. I replaced the 1-2 accumulator and same. In my case, it was marginal fuel pressure. It was ~9psi. Replaced fuel pump and hard shift went away. I assume the low fuel pressure was requiring more throttle than it should to accelerate and pcm delayed shift, shifted hard as it would if I had throttle nailed? I don‘t know what or why but I do know my hard 1-2 shift went away with the new fuel pump. It also really improved drivability and power. I only drive to hardware store occasionally and I guess I didn’t notice the gradual degradation of normal performance. Like gaining a few pounds a year for 10 years…