2002 Ford explorer makes a humming noise from rear and will not shift properly

any speed, all speeds, still a smooth ride, or choppy...shift up or down, (indicates drive shaft/ low fluid), always check the rear diff. fluid, properly, then remessage...

when I accelerate on the highway it doesn't shift up. It doesn't want to change gears at all. It feels as if I have no control at times. It is parked for the moment. My O/D light was flashing, do u think my tranny is shot?

My 2003 V6 was doing the same thing at times. Sometimes it was alright and sometimes the light would flash and it would not shife properly. An acquaintance who owns a tranny shop told me when it happens, bring it to his shop and do not turn off the engine before he looks at it. Turned out to be an electronic thingie outside the tranny. About 50 bucks and twenty minutes later I was back on the road. Good luck.