wsrivers

I have a flashing over drive light on the dash and now it kind of iffy shifting into reverse. I've looked online and some say its a transmission rebuild, some say a silenoid is stuck open, trans mount and even a cable for the gears. Has anyone experienced this and or can give any insight? Some time ago I took it to AAMCO where they cleaned something and the flashing O/D light went off for a few days. Fluid is at the correct level and color. What would cause this not to shift into reverse? Any assistance would be greatly appreciated.