Strange no reverse issue

[Fiddyy]

Hello all.

I have a 1999 C2500 5.7l w/ the 4l80e. As stated in the topic title, I have no reverse. But in doing research I find it's strange that I don't have any other symptoms to report as many other people who have lost reverse do.

Nothing happens when I go into reverse. Exactly like putting it into neutral except the reverse lights come on. Nothing happens when I try to rev it. It doesn't make any noise at all when going into reverse.

Trans fluid is fine, all other gears work fine except when going into 4th or OD (not sure if these trucks are 4th w/ OD or just 4th) the transmission sometimes clunks a little bit. I was told this is just the "locker" engaging and wasn't an issue really that it was common. I am no transmission guy for sure so please let me know if that is a problem.

 

But that's pretty much it. Reverse does nothing except turn the lights on.

Truck has 260k miles and was well maintained by a company it's whole life. Not sure if this is the original transmission or not.

 

I appreciate any input as to what I should try to do first.

Thanks