[Rovernet] Borg Warner 35 Transmission in a 1970 P6 3500S Automatic

[Jonathan Present]

Friends,
I had this Tranny rebuilt 5 years ago, and have only driven 2,500.00 miles since. The Transmission is slipping, second gear not working, etc.

Is the Borg Warner 65 any better than the 35? If so, what is the degree of difficulty to install (modifications necessary)???

I sent it back to the shop that rebuilt it, but am concerned that this trans will not withstand regular use, can I beef up this  Transmission?

Are there any other options, I am aware of the GM/Hydramatic solution, which would require more craziness that I can deal with right now?

Thank You...