'96 Explorer possible transmission problem!

HEEEEEELP!! I have a '96 Explorer XLT TracControl, with the 4.0 v6 engine. While driving like 40-60 kph the gearbox goes to overdrive for a few seconds then shifts back. Plus, i hear some bumping, and my car acts like i shortly pushed the brake. With this bumping noise (like "Clank, clank") i switched to neutral, and does the same, but only at this speed. Anyone knows what is all about? I just got the car, so i have no ideea if the past owner ever changed transmission fluid and/or filter. The car has about 90k miles. I hope it's not the torque converter or the transfer case.... Please help! Any suggestions are welcome!
Thanks!

I had a simular problrem.....My o/d light was flashing too......I disconnected the battery and then replaced it...allowing the computer to reset....It worked....Try that before you do anything else.

Thanks. My o/d light doesn't blink, but i'll try to reset too. Plus i'm thinking to flush the transmission oil. Here in Romania i don't have Mercon oil. Anyone knows if Dextron III is compatible? Thx.

Thanks. My o/d light doesn't blink, but i'll try to reset too. Plus i'm thinking to flush the transmission oil. Here in Romania i don't have Mercon oil. Anyone knows if Dextron III is compatible? Thx.

My understanding is you do not use dex 3 for or with mercon 5.

Hmm, so you say not to use Dextron III? What else should i use? I mean i want to replace the existing oil in the transmission...
Thx

Maybe one of the transmission experts would respond...but from what I understand... If you don't have Mercon 5 available for replacement fluid...then don't flush it....I guess if you just don't have any other option when tranny is low on fluid, you could use dextron 3 ....but I think you would be seting you transmission up for failure by not using Mercon 5....g'Luck

Well I can calm your fears over the fluid mystery (Merc 5 fluid is only used in late model transmissions so your 96 takes Dexstron/Mercron 3!), but the drivability concerns are more of a crisis! :feedback: Do you have 4WD? If so do the 4x4 lamps come on or flash? ABS lamp on? Does the speedometer work? :2cents:

Thanks a lot! Yes i have 4wd. I have no lights on (ABS, O/D, 4WD nothing), i even scnned the car with AutoXray tool, and has no trouble codes, mil lamp is off, only in the "test result" area, it says somewhere "lean upshift" and "lean downshift" or smthg like that. Practicly the only siympthoms i get is that noise ("Clunk clunk"), the short automatic change into overdrive and back to normal between 2nd and 3rd, plus the "bumping" (that feels like when you're running out of gas, and your car uses the last few drops of fuel-you know, the car bumps :) ) THAT"S IT! Everything else works fine! any ideeas about what it could be? THHANKS