I'm towing about 9k lb and truck slows down to 35-40 mph going up 6% grades. I went up the same hills in October at 55-60 mph with power to spare. Then I didn't drive it until March. I installed a new heater core (which has no bearing on this problem), a new crankshaft sensor, and a Fuel Boss pump with a new Airtex pump as a backup. I also washed my AME air filter. After doing all of this I did a test run towing a car on a flatbed trailer from Ontario, CA to San Diego with no problems, 60 mph all the way. My fuel pressure is 18-19 lbs @ idle and 20-21lbs @ 1800 rpm and above. my boost pressure is 26 psi @ 2800rpm and drops as the rpms go down. Any thoughts?

Problem fixed. Just came back from my fall fishing trip and drove 1400 mi and over a 9600" pass with no power problems. The loss of power must have been the unplugged data link from the Edge e-z. With the map plugged in and the data link unplugged the check engine light would not come on and over boost code not set but the ECM would still see over boost and "defuel" the engine.