We sold our Suburban and have replaced it with a 2000 (old body) GMC Sierra 3500 single rear wheel crew cab w/ 454 and 4L80E. We just bought it today from a private seller for a real good price - $3300. It is a rust free arizona truck with a real straight body and very nice original black paint. We are going to make a little hot rod hauler to pull the toy trailers around with.
Anyways, it has a couple things that I would like some input on. Just before the truck comes to a complete stop and while it is stopped in gear it has a slight surge or lunge to it. If it is put into neutral it stops and idles fine. I don't really see the RPM's fluctuating much, but it wants to lunge forward. I am thinking possible MAF issue or other sensor but that was just my first thought. There is not a service engine light on and it does work.
Also there is a slight vibration in the drive line somewhere. I have ruled out tires (even though it needs front tires bad) because the rhythm of the vibration is faster than the tires are spinning (if that makes sense). I am thinking either U-Joints or it feels just like an old truck of mine that had a bad bushing in the transmisson tail housing. I am going to check it out further tomorrow.
I know the 2nd issue will be hard to get input on but what do you guys think about the slow speed/stopped surge?

 

Im thinkin its bad u-joints causing both problems. My 99 Tahoe felt the same way. I felt it right before a dead stop and little jump and right after the light turns green and letting off the brake it would do it again. Replaced the joints and much better now.

 

Do you think it might be the transmission shifting down as you stop? It might help to service the transmission. Sounds like a nice truck. Good luck with it.

 

See thats the thing, when it downshifts, the u-joints with bad play in them will cause it to slightly jolt or clunk.

 

This does it after all the downshifting has already been done. I was testing it in my driveway just inching forward and then stopping and it feels like something is out of balance as you slow down and come to a stop. I can also hear something rubbing as it spins, but it is spinning faster than the wheels are turning so it may very well be the U-Joints. I didn't get a chance to look at it today, but I plan on spending some time on it tomorrow. I will let you know what I find. Thanks for the input!!!

 

That's U joints. I've had that before. You don't have a 2-pc driveshaft, do you? That exaggerates the problem. If you had a jolt shifting into Drive, I'd say that's a motor mount.

 

Bad u-joints can feel like bad motor mounts in these heavy trucks. Im not set on it being bad joints, its just a possibility.

 

Well this one threw me off for sure! Like I said we just bought this truck the other day and according to the previous owner he just had from the head gaskets up replaced - which looks to be the case. I wanted to run a compression test on the motor before putting any money in it. Well the compression was great and there was only a 2 PSI difference between them all, BUT the cheap *** for whatever reason had 4, yes 4, different type spark plugs - 4 NGK's, 1 Champion, 2 AC DELCO's, and an Autolite. Figure that one out! 2 of them looked VERY VERY old. So I went ahead and put a complete tune-up and it is fixed. I never would have thought according to the symptoms that this would have been the culprit. It also had a K&N that was in desperate need of a cleaning. I cleaned the throttle body and mass air flow sensor too, but they both looked fairly clean to begin with. Now I need to fix an exhaust leak (big gasket where the Y-Pipe bolts to the rest of the exhaust) and it should be ready for the road! This was the noise I was hearing. Thanks for all the input guys!!!!

 

The Luck of the Irish Shamrock was with you on that repair..... I hope it continues to serve you well.

 

Wow! Thats crazy. Well at least you got a healthy running motor after the compression test. Good deal Shamrock!