Noisy engine on 2000 frontier

[LeoB]

I just did the heads on my truck, it's a 6 cylinder model.

I had thought I did everything right, but it seems to be making a lot of noise in the top end.

I set the crank to tdc, then installed the heads. I put the timing belt back cover on and then the camshaft sprockets. I lined each cam up on the mark on the back cover as indicated in the manual. I made sure that the new timing belt had all the marks lined up properly with the divits on each of the cogs (the two camshaft cogs and the crankshaft cog).

I torqued the whole thing down in all the steps as indicated in the manual. Then I installed the lifters and rocker arms. Every thing seemed to go together fine. I had marked the distributor before taking it out of the truck. I made sure that the engine was at TDC before marking the distributor. So it should be very close to where it was before.

The truck starts and idles a bit roughly and part of the problem is that I need to torque down the exhaust header, exhaust pipe connection. It's leaking and loud. I set the timing and it seems to be ok.

Now not only does it seem loud, but there is no power in the engine either and under acceleration it seems to be skipping a little, it's rough.

Is there any chance that I'm running 180 degrees out of time. I didn't think that was possible but I don't know. I'm not sure where to go from here.