It would have to be something binding up in the cams if the problem goes away when you loosen the cam tower bolts. I just installed a big block kit that I purchased from HPD two weeks ago. I had it sitting in storage. Are you sure that you are not over torqueing the cam tower bolts? I think they are like 6-8 foot pounds. Do you have the little retainers installed in the cam bearings?
2003Pred; Yoshi RS-3 system, K&N clamp on, Nicolas carb mods,Port&Polished head, Weisco 12.5:1 piston, Nicolas CDI, 14/40 sprockets.
2005 Pred TLD: Quickly becoming the wife's bike.