1998 GMC Sonoma 4.3L V6 Engine Surging?

[NomaSLS4x4]

Just looking for some more ideas on this. My truck surges while driving at around 30-40mph. It surges from like 2000 RPM's to like 3500 and back down right away and then back up to 3500 and back down and so on.

My truck just had the fuel pump and fuel filter replaced by a reputable shop so I know its not that. My catalytic converter is bad and I hear that could cause it and that's what I'm thinking.

I'm also thinking my o2 sensors are going bad so that could be the problem.

Any other ideas? Thanks in advance!

 

[epiphaknee]

If your cat is bad, then it is only a matter of time before your O2 senosors go bad too. So this is always an incentive to replace your cat, as soon as you know it is bad.

I assume you have no codes that are registering?

You will receive codes once your O2 sensors pack it in, so, so far so good...

Replace your cat first and then get back to us!!

Just as an aside: Fuel pumps, even if replaced properly, can go bad quickly. But you can easily test this with a fuel pressure gauge at the fuel rail. However, if it were the fuel pump, you might be able to hear it whining cyclicly as your engine revved and then dropped back down. Replace the cat and then see what happens.