I installed some long tube Doug thorley headers today with the CEL eliminators. O2 sensors are in the right spot. Got new manifold gaskets New crush gaskets from the 2nd cat to the DT header Now it feels like it has a loss of power and slightly hesitates (Boggs)upon acceleration (only from a complete stop) although the the MPG seems better. Things I'm thinking is the problem: The rest of the exhaust is stock, muffler seems shot tho (muffler replacement) I crushed the gasket bolting the DT to the 2nd cat but had to remove it an re bolt it, possible air leak. I didn't reset the ECU, although the CEL isn't on. Does anyone with passed experiences in header installs on 1st gen xterra's come across similar issues and have any solutions? Thanks everyone for your help.