Bought brand new - June, 1999. Responses are posted in the order asked. Current mileage, 28,000+/- .
1. Due to summer heat, didn't notice problem until later in '99. Yes, it does get cool in Miami.
2. Like you, I first noticed the problem when weather started to cool.
3. Once you drive a mile or so, problem disappears.
4. Problem no worse, no better now than when RX was brand new.
5. Dealer has serviced the transmission twice in 28,000 miles w/ fluid changes. One has to assume the dealer uses the Toyota fluid. I didn't expect the fluid changes to change the shifting pattern and it doesn't. Mostly had it done since I tow a boat with it on weekends.
My turn, did u ever try and change the spark plugs?