I have a 2008 F350 with 83,000 miles on it. I have a Magnaflow 4" exhaust, and Diablo Sport tuner. I had been driving for around 40 miles and slowed to make a right turn, when I turn and throttled up the truck stumbled, I saw the the CEL had come on! I could not get the truck above 1700 RPMs. I then realized the truck was in Limp Mode, stopped and checked all fluids, and everything we could. No Change! I went as far as dropping the DPF off, but no help! Checked the fuel filters with no help! Had to limp it on in to home. Left the truck sit overnight, and tried it the next morning! The next morning the truck ran perfect for around 30 miles, then dropped into Limp Mode again! Got any suggestions? I pulled the tuner off to see if this would help, but you good!