Okay Forum Members...I need some serious help.

I rebuilt the C4 in my 65. It was slipping real bad and left me sitting on the side of the road so I rebuilt it. It shifts fine in "normal" driving situations. BUT when I stomp on it, it slips really bad going from 2nd to 3rd. I have to let off the gas to get it to shift.
I found a vacuum leak between the spacer plate and carb after having another issue (long story)!!
I just pulled the pan and there is what I would describe as normal stuff in the pan after a rebuild (about 500 miles).
I have rebuilt a few C4's before without any issues. I did not do anything to the valve body as it looked really good. I'm pulling over 10 in of vac at the modulator.
It is possible that having the vacuum problem caused this again? The engine spooled up pretty good twice when the trans slipped before I parked it for the winter.
Any ideas would be appreciated.