Classic/Antique Car Repair: power glide slipping, Rebuilt transmission slipping

Question
My power glide slips between low and high after 15 min of driving. I had my mechanic change out the trany when I rebuilt the engine 2 months ago, he said he swapped it out with a rebuild power glide. The trany is also leaking fluid. I took the car back twice already and the mechanic said he changed fluids and some adjustments each time but the car is still slipping. any advice?

Answer
If your mechanic is familiar with the way the transmission should operate, but cannot make it work right, you need to insist that he find someone who can figure it out.  If you paid for a good transmission, you should get one.  

I can't diagnose it from here - it has to be done by someone who can test it with his pressure gauges to see why the shift isn't happening right.  There are too many possible causes for me to start guessing.

Dick