1996 Gmc Sierra Problems

My first post here:

1996 GMC Sieera SLT 4x4 ext cab short box, 100000 miles

Problem #1

I have only owned this truck for 6 months. When I first bought it the motor was silky smooth. Gradually it has developed a rougher feel when accelerating(under load). It seems smooth at idle but seems to almost vibrate thru the pedal when you are accelerating. The vibration is related to engine RPM. Any ideas.


Problem #2

Also a problem that was not there when I purchased this truck and is slowly getting worse. There is a clunk that can be heard sometimes when the auto shifts from 2nd to 3rd. Nothing between 1st and 2nd.


Any help would be greatly appreciated

Thanks

Most likely you have developed an engine missfire under a load.
At 100k these trucks are due for a tune.
I would recommend having the ignition system scoped to find if you are having a secondary ignition breakdown.

As for the clunk my 96 did the same thing. Dealer said it was normal and the more people I talked to with the same truck said theirs done the same.
As for the vibration, Did you happen to have a U-joint Fixed? I did and the dummy bent my driveshaft. Replaced the shaft and it went away.

Information on problem #2
Information on 2-3 Upshift or 3-2 Downshift Clunk Noise #01-07-30-042A - (11/26/2002)
Information on 2-3 Upshift or 3-2 Downshift Clunk Noise
2003 and Prior Light Duty Trucks

with 4L60E or 4L65E Automatic Transmission (RPOs M30, M32)

This bulletin is being revised to add the 2003 model year as well as information about 3-2 downshift. Please discard Corporate Bulletin Number 01-07-30-042 (Section 07 - Transmission/Transaxle).

Some vehicles may exhibit a clunk noise that can be heard on a 2-3 upshift or a 3-2 downshift.

During a 2-3 upshift, the 2-4 band is released and the 3-4 clutch is applied. The timing of this shift can cause a momentary torque reversal of the output shaft that results in a clunk noise. This same torque reversal can also occur on a 3-2 downshift when the 3-4 clutch is released and the 2-4 band applied. This condition may be worse on a 4-wheel drive vehicle due to the additional tolerances in the transfer case.

This is a normal condition. No repairs should be attempted.

Thanks for the great info. I am curious as to the signs of a bad TPS. It seems to me that a faulty tps could make a motor run rough and alter the shift pattern. The reason I question this is that at the same time this truck started to run a little rougher I noticed this clunk. It wasnt present befor this time. Plugs are new and wires measure good.

Thanks