2002 3500 lb7 with a Allison 1000 and I put all 3 new trans cooler lines on it from GM and started getting a p0872 transmission fluid pressure switch circuit C low code and MAP sensor code. Truck goes into limp mode when switching to (D). Changed map sensor and trans fluid pressure sensor and neutral safety switch and new filters and fluid in trans and still doing it. I'm stumped and need help my friends. Old fluid was not black or burnt smelling or no clutch fibers or metal shavings in it. Truck trans had never slipped or shown any bad signs. Some people said it was a broke wire or a TCM. I'm stumped bad. Any info is very appreciative my friends. Truck has 240,000 and a s&b cold air intake and 4inch exhaust and EFI live. But never been turn past 3. Only when pulling a camper it was turned on 3. But stays on 1 or 2. Sorry for the long post my friends.