94 Chevy with a Shifting PRoblem

I have a 94 chevy silverado 5.7 350 2wd. I drive it and it runs fine all of a sudden the check engine light pops on and it shifts hard. The funny thing is it doens't do it all of the time. I am trying to figure out what it can be. Can some one help me.

I had a 92 that did something like that, but it was a manual trans so i dont know if it would have made a diff in the shifting or not. But it turned out to be the knock sensor on the right side of the engine had a bare wire and from time to time it would ground itself out on the starter. Repaired and rerouted the wire and it never did it again. Hope that helps

First thing is to read the code. This will help for that: http://www.troublecodes.net/GM/

Most likely you will find P1870 (or the OBDI equivalent) which indicates the PCM detected the tranny slipped. When this happens, the PCM commands the line pressures to increase to protect the tranny and give real hard shifts.

Most likely the TCC regulator Valve or TCC Apply Valve is leaking in the valve body; although, other issues can cause the slip code.

Find out what codes are stored and go from there. After that, the valve body will need to be inspected if the code is a tranny slip code.

//2000CAYukon