What transmission is it,? On the 545rfe it has a shift solonoid that is probably bad or sticking. Transmission is ok I would think.
if it's not slipping. https://youtu.be/vaUJ18obqcA
this is solenoid and I replaced them before.

 

Not sure what trans it is, 4 speed auto, 2000 4.7 Dakota club cab, no tow package, 2WD. It's my primary ride for the time being while I get my Subaru's suspension sorted, but once the sub is back on the road I'll get the pan off and see what I can find in there.

2 filters in there? Looked like a normal one and a screw-on one from the video.

 

It's a 45RFE in 2000.

Yes, two filters. Get them from Dodge. Lots of people have trouble with aftermarket filters sealing and if they leak, you don't move.

 

The aftermarket spin on filters also don't have an anti-drainback valve.

 

I had odd tranny shifting issues when cruising for a year before mine did basically what yours did: jumped down a gear or two on the highway all of a sudden. Scared the hell out me. Finally threw a code though, and it was the TPS. Changed it and no problems since.

 

Was it very hard, violent shifting?

I went to get the filters today, dealership guy told me there was only one in there after a little eye roll, then came back with two part numbers... I'll get them somewhere else, and $62 is gonna have me wait for another paycheck.

 

During my most recent cooling system debacle, my mechanic neighbor is over watching me break stuff, and I'm checking fluids, and he says "you gotta check the trans fluid in neutral, Chryslers don't run the pump when the truck is in park"

Huh?

Sure enough, on the stick it says something about check in neutral

Turns out I was about a quart low, so I poured one in and drove it about 300 miles, no clunking.

I'll still do the trans service to be safe after things settle down, and I'll report back if it clunks again.