header on 96 tacoma

I have a 96 tacoma 2wd. I noticed my exhaust was a little loud for a 4 cylinder so i looked under my hood at my exhaust manifold. I noticed a long crack right down the center of the manifold. I decided i would replace it with a header because the price is about the same. My dad and I put the header on my truck. We had no problems getting it on there(except for a few studs coming out). The header was a perfect fit. My truck ran great for about 1000 miles. After that, it started sputtering constantly when it was cold until it got hot. It got to the point that I couldnt run it because it sputtered all the time and it would die.( it had an exhaust leak by the pipe but was fixed) I took it to my mechanic and he checked everything (timing, spark plugs and wires, fuel filter, fuel pump, MAF ect.). Everything was fine. I ended up taking my header off and putting my exhaust manifold back on. It ran fine after that. All of the sputtering stopped. I dont want to keep having a cracked manifold on here and i dont have the money to by a new manifold. Does anyone know what the problem could have been with header??????? Please let me know..

All of the new gaskets i had were paper gaskets. I dont know if that would have anything to do with it. When i put my manifold back on, i used copper gaskets.

did your truck knock or click while the engine is cold? that is while accelerating

It would knock while i accelerated. It would stop sputtering after i raced the engine up for a while, but it got to the point that no matter what i did it would sputter the whole time. I took it to a mechanic and he gave up on it. He couldnt figure it out

FYI... I had a Downey header crack in the middle of the pipes at the collector. Downey wouldn't warranty it. I bought an LC Engineering header for less than the Downey and it has been great. It uses the Toyota OEM gasket at the head and is ceramic coated stainless steel vs. Downey ceramic coated steel. I have had it for several thousand miles with no problems.