Recently bought an '08 Buick LaCrosse w/92k miles. It accelerates normally up to about 15% pedal position, then it stops increasing from 15 to about 30%. If you play with the gas, the engine does not respond. Once you get to 30%, it downshifts and powers up. My theory is that the APP (Accelerator Pedal Position) is worn or shorted, and gives a faulty signal in the 15 to 30% range, having to use the default last valid reading. I have read that some sensors can fail within the valid range and not give a fault reading on the OBD. Sound about right?