If any of those things don't work, take a look at this. Bill, you had actually suggested this to me when describing the same symptoms as the OP.

"You may find that revving the* engine up will finally get the car to move and it will BANG into gear. This is because the pump in the transmission is working harder and moving more fluid thus allowing the added fluid to overcome the leak which prevented the clutch from either initially applying or staying applied."
No Forward Cold