URGENT HELP! How to check used tranny on truck?

[hoser45]

I'm looking to buy a used 2000 F250 7.3L. It has low miles, just over 100K but dealer has no service records (bought at auction). Everything in photos look good, but is there a way to check tranny to determine if anything is bad or may be in need of a rebuild of some sort? What should I look, listen, or test (and how to do it)?

If I go forward, I'll probably take to a mechanic to check, but looking for ways before spending money for a detailed inspection. Thanks!