no leaks. everythig i hooked back up. new plugs/ wire etc... it just has a giant flat spot. Will try the TB spacer.
it's prob just the power band of the engine now with the header. to make the power in low rpm you will need to get a cam to match and even then it may not make low end power. headers are to improve top end but you will loose torque at low end it's a trade off. re-gearing to bigger gears like 4.88's help to keep the rps up there also.
unless you do have some type of running problem? you said it ran like crap before you changed the manifold? or was it just noisy from the leak?
hope it helps. if not my advise is find a stock manifold that's not cracked and put it back on and see if you prob is gone if it is it's the power band of the header.. and if your not happy with the power band of the header you will have to just leave it stock.
I like having my power at higher rpms and just keep it in the 3-4000rpm range and I run 4.88's to help keep it up there. and someday hope to build up the engine I have with heavier springs and harsher cam to improve top end mid to top end power!!
hope this helps.