6.0 swap trouble shooting! please help.

I recently swap a 5.3(lm7) with a 6.0(lq4). When I bought it to a local shop to get dyno tuned, We discovered that it had misfires like crazy on serval different cylinders. The vacuum was never constant, And the long tube headers would turn red hot. This all happened in idle.

Its a lq4 with 862(5.3 heads) ported and milled with 59cc cambers, making it 11:1. I put a TSP 228 cam with 7.400 pushrods and comp 918 springs. 28lb injectors, stock intake manifold.

Are my pushrods too long? Did a lifter collapse?

Thanks in advanced. Merry Christmas!