Some busy work to do on several things there...

Do you know which Transmission you have ?
In 89, there were several which could have been mated to your 7.4L engine.

Ref:
https://en.wikipedia.org/wiki/Chevrolet_Suburban

 

I do not know as of right now but ill ask the guy who i purchased it from. should also be able to check the markings on it to confirm.

 

Good, and yes, "trust but verify"

I was hoping that one of the Tranny Guru's would have made some comment by now, but maybe an ID on the Tranny will encourage someone.

In all hopes that the accident didn't really screw the Tranny up, my first thought was since it may have been sitting for a while, plus wobbled around when placed in the new chassis, that you might try just running a good Cleaner through it, to see if some trash might have got it gooped up and reluctant to shift. Might think about trying that first.

 

that sounds like a good idea. seems like it might be a long shot but the most complex problems have the most simple solutions. lets hope so! it was sitting for a bit. ill you know.

 

Had some time on my hands today, and read back through the Wiki link I gave you. So, its not several transmissions, but just two !

A 4 speed and a 3 speed. Since you haven't been able to make it change to third gear yet, that doesn't help ID it. When you do run that cleaner through it, make sure it's full of Fluid. That slipping you mentioned makes me think it may have been a little low.

 

well its leaking transmission fluid pretty bad. i might bring it in for a troubleshooting.

 

If it's a Rear Seal, that's quite easy to DIY
It's helpful if you have an Installing Tool.
If not, those can be loaned/rented from some Auto Parts Stores.