I just loaded up 2.4 in my APM 2.5+ and went through the calibration process and set the throttle parameters and am experiencing unexpected behavior for the throttle. When in manual mode, steering works as expected, albeit courser resolution, but throttle does not work correctly. When moving the stick forward, it jitters the wheels but does not move it. When moving the stick backwards for reverse, it only has one speed, fast. It didn't matter that I reversed the channel on the radio or MP, the behavior was the same.
If it helps, I'm using a Spektrum DX8 with an Orange 6 channel receiver. I made sure the truck was properly trimmed and the ESC was properly calibrated before adding the APM.
Any ideas? I had something similar happen last year when I tried using the APM 2560 and IMU last year using Traxxas radio gear but chalked it up to the radio.