Need some 700r4 help

[Tiger Joe]

Truck is an 87 4x4. 5.7 700r4 np208 I believe.

So I’ll start by saying I don’t drive the truck much. I frame off restored it 20 years ago, it would be lucky if it has 2,000 miles total in that time. The engine was rebuilt at some point, trans and transfer case are original. Was my dads he never abused it so there was no need.

Last fall I drove the truck, probably October and had an issue with truck not shifting correctly. Honestly I don’t remember what happened. I played with adjusting the tv cable drove truck it was fine so I never looked at it.

Fast forward to this weekend, I pull the truck out of the garage for the first time. No issues at first. Started and pulled right out. Soon as I go to pull out of my driveway, it’s like brakes are locked. Truck doesn’t want to move. I play around and bam truck moves no issues.

When I’m driving I notice the truck is only shifting at 3,000 rpm. And once driving and you stop, it won’t go down into first. On a few brief moment I swear it feels like the front end bucks, but it happens so quickly I can’t be sure all the time.

I never messed with a 700r4, so where do I start? Google machine says governor, tv cable, or the throttle valve in trans is stuck? I guess that’s what tv cable hooks to?

I’m also thinking I’ll drop pan and change filter. That will let me check fluid plus it’s been 20 years so it’s due.

Any other ideas based on my symptoms?