This vehicle developed a transmission code which prevented necessary emissions approval for registration. In short time, it began shifting abnormally. It was taken to a mechanic who "supposedly" rebuilt the transmission...I have since been informed that for what I paid, it could not have been a complete rebuild, as what I paid would not have covered the parts, let alone labor...Within a few months or less, it quit working. I returned it and was told that anti-freeze leaked into the transmission. It would need a new radiator, etc,..and they would handle the transmission rebuild under warranty. Upon return, within less than 500 miles, I was driving approximately 55 mph and began slowing to down to identify the name of a road...realizing it was not the road I was looking for, I pressed the accelerator to increase my speed only to realize that it was like it was in "neutral"...the engine rpm's increased, but no vehicle movement. The shifting linage is connected and working...it will go in and out of "park" and not move...all other gears are like in "neutral". The mechanic no longer wants to deal with the issue...which I am obviously fine with...I feel like that there is someone out there that with experience that have a 50,000 foot view of my whole situation and has an idea of what may be wrong with this vehicle. I have had transmissions go out gear by gear until it would no longer move...this is NOT how the vehicle responded when it quit this last time...

 

The water getting into the transmission could occur if the transmission cooler inside the radiator started leaking. I've never seen a report of this happening so I don't know what symptoms to expect from that but I can't see it being good. Much of the transmission is basically a big fluid pump and without proper lubrication from the transmission fluid, the seals could all be ruined. Did you notice anything in the coolant that could have been transmission fluid? Have you seen any evidence of coolant mixed in with the transmission fluid?

It sounds that you likely had a poor quality rebuild and then separately later the cooler in the radiator failed allowing coolant into the transmission ruining the transmission. Coolant getting into the transmission would be bad to catastrophic for any transmission, whether a new or a quality rebuilt one.

If you want to keep the truck, it likely needs a proper diagnosis by a transmission shop. The replacing of the radiator is something they could pretty easily do.