Wow..just pulled the exhaust mani gaskets and they were burned completely through and my whole head is pitch black. That's a hellacious leak

 

I had some what of the same issue on my last set up. It would idle ok and would drive fine but would bog under any load. It would also backfire thru the exhaust and into the intake. Probkem ended up being the injectors. If you havent done so, take them out and see if they are not clogged.

 

what size were your injectors again? didnt have time to go through the whole thing looking for a answer..

set of 8.1l injectors - 200 shipped
fast 65lb short injectors 300 shipped