Just came across your post for the same problems i'm having on my 95jimmy on google, so i joined this forum to see if you or anyone else can help. I have the exact same problems and engine (vortec v-6) you had in your 8-21-2009 post, with negative ignition timing jumping all over the place. It came on suddenly-driving around the block and just like that, flashing check engine light and rough idle. On cold start up no light and no codes,but rough idle-then drive a block and engine light. No decent manuals on this but Haynes-So i've checked and replaced the spark plugs and wires-cleaned the cap and rotor-replaced the crankshaft position sensor (no resistance)-then the camshaft sensor in distibutor all with no luck. Am about to replace the right side knock sensor but i doubt if this will help. Have checked/cleaned all my grounds. Don't know where to go from here-think maybe my pcm needs reprograming but want to find out what you did, if i can. Work 6 to 5 so,i can't reply immediately

let me tell you what happened mu tranny dipstick popped out and fluid spilled on motor some wires caught fire drove home but it would not go in reverse spliced and sodered wires drove next day fine but the folowing day it would not move forward or reverse added fluid level may be a little to much cause i coundnt see it on dipstick at first how do you check line pressure.

I have a95 with w motor engine running rough and had poor fuel mileage went ot shop to get checked out found the passanger side gasket sticking out of manifold so replaced them with apex gaskets and installed new aus spider in it .