98 5.7 gmc stumbles

[timssail]

The engine stumbles at low RPMs 1000. it acts like it does not know what gear to be in between 1st and 2nd. As soon as i apply more fuel it runs fine. the truck idles well. I can step on the brake and try to make it stumble but the engine runs smooth and no miss. Codes are 0404 0405 (egr) that is new. I did replace the left Cat. It fell apart. The right side is still original. This truck has a dual exhaust with a flow master. Cleaned the throttle body intake and the new dist cap. Checked the plug wires they are new too. MAF is new. The plugs have not been changed, that will be my next step. I can not get any codes other than the EGR 0404 and 0405. Some new codes came up P0141 P0161 O2 sensors could be related to the stumble so maybe a plug change will help plus the new EGR. will post results. The O2 codes are not consistent.

[timssail]

I changed the old Napa EGR valve with OEQ Valve and the hesitation is gone. the EGR code did not come back yet. We will see how things react this weekend. so far so good.
there was a burn mark on the old gasket between the two ports so there was a leak between the two port holes. the NAPA EGR valve was new last fall.

[PeteA216]

Clear your codes and start over. That way anything thats no longer a problem will be gone out of your code "list" and will hep you to narrow down the problem(s) you have.

[timssail]

EGR removal is easier with a 6 to 8 inch extension with a universal joint, 10 MM socket and some tape to hold the gasket on to the EGR flange. the left hand bolt will tend to cross thread without the universal joint. scotch tape is just enough to hold the gasket and should not affect the seal. Thighten the bolts to just "snug" the flange is prone to cracking if the bolts are too tight or uneven.

thanks to all for the advice.

Tim