'99 2500 engine shutter (buck)

[Markf]

Gentlemen,
I have a 99, 2500, 4x4, auto, 6.0L with 64,000 miles. The problem that I am experiencing is that at approximately 45 mph, transmission in 4th, going up a hill, the engine will start to buck. If I manually down shift it to 3rd the problem goes away, or if I hit the gas to force the down shift to 3rd or 2nd, the problem goes away. It is very similar to leaving a manual trans in high gear when coming to a stop.
Also, sometimes when pulling out of a side street and I need quick acceleration, the same problem may occur!
Is there an adjustment or is this a computer thing? :confused:
Your help is appreciated.
Mark

[Eric 1]

I assume its a chevy?

My first thought when reading your post is that it is in your tranny, torque converter slipping. Or it could be a computer malfunction net letting it down shift at the right time. Can you feel they engine surge or lose or gain rpm's? does the check engine light come on?

Or maybe a fuel filter is plugged?

[Smalltimer1]

We had a truck to start bucking in OD and turned out it was skipping and ended up witha bent pushrod.

[Markf]

Yes, it is a Chevy.

Wouldn't it always buck if a push rod were malfunctioning, since the exhaust or gas valve (depending on which one) would not be seating properly at all times?

Also, the engine light has not come on and stayed on. It may have come on while the problem was occurring, however my eyes were on the road.

[xcopterdoc]

Sounds like torque convertor shudder. In otherwords, it cant make up its mind if it wants to be locked in or unlocked. Have the tranny filter changed and the tranny flushed. See if that helps any.

[UNISCAPER]

One other thing to run down....The illustrious electroic shift trannies will send out a message to the computer to kill the ignition for a milisecond until the tranny shifts. If it hangs up and is not responding properly, it will act similarly to how you describe.

Pay to have a dealer diagnose it, then determine how to repair it. There are too many variables without seeing a scan of your system to determine anything rigth now.

[Markf]

Thanks to all the info. I'll let you know how it works out.
Happy Thanksgiving