So let me cut to the chase here. '99 4Runner Limited, Automatic, 141,000 miles. Had been my DD up until a month ago when I bought a car for the chore of DD'ing. Never had a problem, always well maintained. Had the transmission serviced less than 8000 miles ago.
Early last week I back out of my driveway to re-park my 4runner which had sat for 5 days undriven and it could barely drive back up the 15 feet of driveway. It acted as though the parking brake was on, but it wasn't. I repeated the process again with the same result, 4runner revving up but hardly moving at all for the amount of engine speed. I backed down a 3rd time, sat at the bottom of the driveway a minute scratching my head, and began the climb up the 8% grade again. This time it drove as normal. I took it for a 15 minute drive after that and it showed no unusual symptoms, and later took it for a drive into the hills to gather firewood for a weekend camping trip. Drove perfectly.
It sat for 4 more days until Friday. I packed it up and when I left to fuel up, again I didn't let it run for more than 25 seconds before leaving the driveway, and once again it would barely move down the road. I pulled up to the curb outside my house and sat for about a minute, pulled away from the curb and it drove normal. Fueled up and took off on our 400 mile trip, and it hauled it's 5500lb mass up long steep grades with no signs of any issue from the transmission.
Anyone have an educated guess as to what this may be? So far it only happens when it has sat for several days, and when it's driven cold.