Not taking away from modders - I know some great ones to, but I would just buy a new engine, there is not one on the planet that can provide a sure answer to what wrong with it. and buy the time they CHARGE you to test and shipping and this and that mod there is no garuntee that it will be fixed.
At worst send it back to OS and they will charge you like 200 and send you a new one......... do you have the reciept from when you brought it...
I fell like if I cant feel confident in a certain part of my truck then I will not be happy at the track.