Sputtering when at full throttle
 

Hey guys I have a 1996 Ford F250 with a 7.3L Powerstroke. I got it back in January and it was 100% stock. The truck was showing 355,000 miles when I got it but I think the motor and tranny were replaced at some point. On the way home from picking it up it would sputter a little when I put it to the floor. I took the exhaust from the turbo back off and put a 3" down pipe on with a short 4" into 5" pipe and a 6" stack so she could breathe. I then put a TS Performance 6 position switch in her basically for fuel mileage and power when towing. The truck runs and pulls like a beast and has made me a believer in the Powerstroke motor. My only problem is that she still will bog down and sputter at full throttle unless I run Lucus Fuel Cleaner. I thought it might be a stuck injector or valve but I don't want to go tearing her down and risk causing another problem in an older truck unless I'm sure of the problem. Any thoughts on what it might be?