After being parked for 3-4 days, when first started and placed in drive or reverse, the car will just sit there with no indication of transmission engagement, tap the gas --- nothing. After ten seconds or so car will drive and shift normally. If car is driven every day problem doesn't show up. If car is first shifted to neutral and allowed to idle after being parked for days it acts normal on first engagement. I have to believe the lack of pressure on the clutch plates is causing undo wear when first starting out without adequate internal pressures. Any ideas of whats causing the problem? Is there a check ball allowing the fluid to drain out of the pressure areas or torque converter? Acts like it. I have changed the oil and filter. Used name brand Toyota transmission fluid. Didn't make any difference.
From what you are explaining to me, it sounds like the torque converter is leaking down while the car sits for a few days. The problem would probably be related to the seal inside the torque converter or the seal on the tip of the input shaft.
The only way to check this is to do a pressure test on the transmission when it is cold. If you start the vehicle and you don't have any pressure for about 10 seconds then this would indicate no fluid in the torque converter until it pumps up. When the converter is filled the pressure will be in normal range and transmission shifts normal.