I have not experienced this but my wife has ...... here is her description.

This is a 2004 Suburban LT with the 5.3 ... no flex fuel. Randomly when driving she feels like the car is still moving forward but losing power. The tach slowly drops and she feels a mild bucking / sluggishness in the truck. The truck never dies and recovers but its still a very concerning problem for me since she drives it a lot and also takes our kids everywhere with it.

I bought this a few weeks ago (1 owner truck) and he said that he recently replaced the fuel pump, battery and I tested the alternator and it looks good. I also recently verified all vacuum lines are good (visual inspection) replaced the MAF sensor and air filter. There are no codes posted or pending codes in the computer so I am not sure where to go next.

Any advice on what to look for? Crank position sensor, fuel filter, fuel pressure even though the pump was replaced, coolant temp sensor, etc......

thanks,
-Steve

 

Ask the previous owner if the replacement fuel pump was a GM one as some aftermarket ones aren't reliable. Also check the fuel pressure.

 

I could not get in touch with the original owner but i did test the fuel pressure ..... with ignition on and truck off pressure hits 60, drops to 55 and then holds there and slowly drops another 5 PSI over a long period. With the truck running the PSI stays tight between 60 and 62.

I replaced the battery with one from my Silverado since i suspected it was bad and the rough idle went away. First drive the hesitation / bucking problem was still there just not as bad. I put it in tow haul mode and the problem went away fully. I then put it back in regular mode and the problem has not surfaced. Could a bad battery or battery connection cause that type of issue? What does changing from tow haul mode back to regular mode do or was that just a coincidence?

 

The tow-haul mode changes the shift points and holds lower gear when going down hill.

 

Well I found the root cause of both my problems ..... a bad battery. I put a platinum AGM in and the voltage fluctuation and bucking / hesitation is all gone. Never thought a bad battery could cause so many issues.

 

Thanks for reporting your solution back to the Forum. That might help others in the future.