This isn't on a Dodge, but it's more general automatic tranny knowledge than anything else, and everyone on here seems to know more than most other forums.

A few days ago, the Explorer stopped going into overdrive. Then, today, it stopped going into 3rd, and it will barely go into 2nd. Is the tranny shot, or could it be like a valve body or something?

 

My experience has it that if the engine revs but won't make the transmission make the truck move, it is the bands or one of the friction surfaces.... the trans is shot.
If it won't shift properly it is the valve body or a speed sensor. If it is a speed sensor the truck will often shift normally for a bit but then go into limp mode. The valve body thing, for me, has been the equivalent of a shot transmission. No point in disassembling the transmission to work on the valve body and not do a complete rebuild
hope this helps

 

Check the tranny fluid level and look for metal shavings (wipe fluid on a white cloth and look for black friction material).

If that checks out ok, check for codes and make sure all connectors on tranny are plugged in.

I am betting a sensor went bad. Might be worth asking some local shops what the problem may be. It might be a common problem that they have seen before.

 

Tranny fluid seems clean. I just checked the codes, nothing for the transmission. I'm betting it's a valve body...

Thanks guys.