96 blazer misfire in first gear?

Hello. My 96 blazer is I believe misfiring at the top end of first gear. Once the revs are up over 2000 I get a couple of chugs that feel like a misfire then it goes into second gear and everything seems fine. I had a engine light on for random misfires, and a P0420. I went ahead and changed my egr valve, the cataletic converter, the 02 sensors, and the PCV. I also ran some seafoam through the brake booster and ran some injector cleaner. The guys that put the cat on cleared the engine codes, but I still have the chug at the top of first. I have not driven it except home from the shop to see if another light comes on. I am going to take it for a spin shortly to find out. I am out of ideas of what else to change though. Wires and plugs have about 15000 on them. Cap and button were causing the misfire I think that blew out the cat. I changed those about 1000 miles ago. The truck ran a hell of a lot better but still had this little miss at the top of first gear. Any help would be greatly appreciated.

Just got back from my drive. Got a code P1406. I believe this is a EGR code. I got mine at a salvage yard. Is there a good way to clean them up, or do I just have to break down and pay the $175 for a new one. Is it possible that this is the reason I am having the problem? Thank you

Is it a 4.3 W engine
Remove and clean the end of the egr valve and look for a carbon chip/ball under the egr valve plungers.
Clear codes and drive and recheck for codes.
Watch close for any more miss fires present or history codes or any other codes.
What kind of spark plugs are you using?
How is the fuel pressure?
Also get a reading on the camshaft retard setting