<VV> Power Glide Problem

[Eric Kirven]

'63 Coupe with a pre '64 power glide.
Car will move in forward and reverse but will not shift into drive until 
it has been driven 8 to 10 miles.
If you continue drive it shifts fine. It you are doing errands and let 
the car sit for 1/2 hour or more the shift issue comes back.
The original transmisson was replaced with a spare that was know to 
good. It had a fairly good leak until the front seal resealed itself 
after about three weeks of daily driving then it quit.

A new vacuum modulator was installed after it was tested.
A pressure test has NOT been done on the front port.

Any ideas what the problem could be?

Thanks and HAPPY NEW YEAR!!!!.

Eric