Let me start out saying that I live NY, and the weather varies quite a bit from one season to the next as you might imagine. Consistently, my 1999 es300 needs to warm up to about half of the operating temperature to shift into overdrive. After it has shifted, all is well and you would never know there is anything wrong. In the winter however it takes much longer to finally shift into OD. After 120,000 miles, it finally stopped shifting into OD all together. A possible related issue is the CEL coming on for a lean mixture. This issue comes rarely and normally just goes away (the bucking and CEL light that is).
I found a post from the past that seems like it might be what I have but the poster never said what part it is...
"Lexus01,
Thirdly, the transaxle is designed to not shift into overdrive until the transaxle fluid has reached 152 degrees. This is to prevent premature wear in the tranny and get the engine up to temperature faster so it meet emissions requirements faster. If this concern is particularly noticeable in colder weather, this may be the problem. Note: please make sure the fluid you used in the tranny is the Toyota T-4 fluid. According to the engineers, the wrong fluid will lead to slippage and possible failure.
The only oddity is the general misfire code(p0330). This could be an entirely different problem, or ist may be related to the dumping of too much fuel into the engine.
Let me know how you make out.
Good Luck
Lexasm "