From what you describe though sounds like a belt. Have you ever had belts do that on you? If so then you'd know. Hmmm. thats a tough one if it aint the belt.

 

I know it's the belt. for some reason the ribs on the napa belts aren't that deep, so I am just assuming they don't grip as well as others, plus, unknown mileage/abuse on the tensioner, I'd just as well have the belt slip like that than put the shock of the instant rpm shift into the accessories, my 97 4.3 S-10 5 speed does the same thing if I dump the clutch when catching gears (napa belt too).

I don't feel it's a problem, just the programming has pretty aggressive shift pattern, going into third it's right on the verge of chirping the tires when you are 1/3+ into the throttle, so you know the motor is going from around 3-4 grand down to 1-2, I could soften the shifts up, but tooling around easy on the throttle if shifts like stock.

 

The Goodyear belt is supposed to be 100% better.

 

IS THIS VIBRATION PROBLEM BEEN SOLVED YET, IF SO PLEASE LET ME KNOW WHAT YOU DID, I'M HAVING EXACT SAME THING.

 

No I haven't figured out the problem yet. I just replaced both motor mounts think that might have something to do with it but it didn't change. I am now thinking that my harmonic balancer is probably worn out and is causing my problems. It does have 110k on it. As soon as I can save a few bucks I will be getting a new balancer.

 

i dont know if you changed it yet, but have you check, balance or replaced your flywheel yet?

 

I haven't replaced my flywheel, but I did get a keyed crank hub from thunderracing.com and I changed out my converter. it seems better, still feel a little vibration, don't know what it could be..