Engine stumbling or torque convertor problem

I have a 99 2500 suburban with the 5.7L engine...145,000 miles. Under load the engine or tranny is stumbling. I can't tell which is happening. The plugs are good, I put in new plug wires and at idle, I'm getting good spark through my timing light on each plug wire. When the truck stumbles, there seems to be a slight "shudder" which might be the torque convertor?? The tranny isn't slipping where the engine revs up. Or, if the engine is missing, would the tranny sense this with the torque convertor trying to compensate? I'm not sure how to diagnose what's going on?

Any suggestions??

Thanks!

I forgot to mention that last summer I replaced the fuel pump with an aftermarket. Soon after replacing the pump, it began to whine so thinking there might be restriction causing the whine, I replaced the fuel filter as well. The pump continues to whine so now I'm beginning to think that it might be a fuel problem. How do I test for proper fuel pressure?

Last summer, I also had the tranny flushed, including new filter. The fluid looks good and red and up to level.

Any ideas??

Thanks

when you replaced the pluge did any of them look really bad or are they all the same?

Last summer, I also had the tranny flushed, including new filter.

There is considerable debate whether a flush on a high mileage tranny is a good idea, especially if regular flushes have not occurred. Some feel it does more harm than good by removing dirt that aids in shifting in a worn out tranny.

Perhaps there is something to it in your case.

Don't know if you saw my posts: '96 S'brbn Transmission "Slipping" ?
Thought my trouble was trans but replaced the fuel pump and good as new. Sounds like you did that last year but...check the post. About 10 or 12 posts down from this one...

Steve in VA

I purchased the suburban with 92k on it, so at 135k I replaced the plugs after noticing a slight misfire. Didn't notice that any plugs were fouled or different than the rest. I had Expert Tire, a local Firestone dealer do a diagnosis (145k miles) and they told me this is a no brainer...the plug wires were bad but this didn't solve the problem. They also told me the plugs are ok. I haven't personally pulled them to look.

Interesting info regarding doing a tranny flush on a high mileage vehicle. I don't know the history if regular flushes were done or not.

I've read the posts on the 96 tranny slipping and I am thinking this might be the problem...fuel pump. I put an aftermarket fuel pump in last summer and it has been howling ever since. Can someone advise how to check for proper fuel pressure??

Thanks

To check the fuel pressure you need to hook a tester to the valve that is on the drivers side of the throttle body. Then turn the key on and watch the pressure guage, the pressure should be 60-66 psi with the key on and engine off, if the pressure drops rapidly after the fuel pump quits you may have a bad fuel pressure regulator