94 GMC shudders under load

My 94 GMC (extended cab, 4x4) has a problem where it shudders under load. You really notice it in overdrive and you start to climb a slight incline or accelerate slowly. Just before it kicks down from OD the whole truck shudders.

Lately it has gotten to the point where it does it in D too. I can be cruising along at 100 KMs/hour and if I try to slightly accelerate the whole truck will start to shudder. It almost seems as if it may be related to throttle position and/or vacuum pressure.

I'm pretty confident that it is not the transmission...it seems to be very solid in the shifts and have had no other problems. The fluid is up and clean and the tranny filter was done about 30K kms ago.

When I first started having this problem I had a whole tune up done (plugs, wires, cap, pcv, etc) and no fix. It is slowly getting worse and easier to duplicate when driving. It's gotten to the point where I don't use OD any more becasue it is so much worse in the higher gears.

Oh...and new fuel filter in there too.

Any suggestions appreciated.
Steve

Check the vaccum hoses

Yeah, I've gone through them pretty thoroughly but also pretty sure i can hear a vacuum leak right at the throtle position where it starts to shudder. I need to get a good pump so i can check them without any engine noise.

Thanks

I had a simmilar problem :after I installed a throttle body spacer , at low RPM it felt like its downshifting and upshifting right back and I found out that the problem was a faulty vaccum hose.After replacing the hose nomore problems

Interesting... I put a throttle body spacer in mine two years ago. This shudder problem only started a year ago and has progressively gotten worse. However, could be that one of the hoses is too tight now and is slowly deteriorating or something from being too tight or redirected because of the spacer. I'll have to have another look.

Thanks

There is one more thing. Do you have a kick down cable? If you do did you adjusted after you installed the spacer? That might cause the problem too

Hey do this put preimium gas in it and see if it does it. If it goes away it is timme for a top engine clen do to carbon deposits. Just let me know and I will tell you how to do this

since you have had the tranny done has this problem become more prevelent. check the flex plate to torque converter bolts. if they are loose this will cause the truck to shudder and will get worse . if the bolts did come loose make sure to check for cracks in the flex plate. some gm's are known for this problem.