If you checked your fuel injectors....then...duhhhh i'm lost! that would have been my guess! have you had any problems with it overheating? Cause when i had my old truck and i blew a head gasket, i was running on three cylinders(sp?) and that's y i was lossing power and i couldn't get any power at all, not that a 4 banger truck has power...but less than what it started with, kinda sounds the same as your problem...
