Although this post is quite old, I don't mind it being resurected!
The 1-2 shift in my 01 Lexus RX-300 are unacceptable when cold. Even on summer days in the 80-90 deg days. When the engine is first started, mirrors, seats and belts adjusted B/4 taking off, the 1-2 shift seems not only lazy but confused. After that, most of the shifts seem pretty normal as the vehicle warms up. Driven slowly on that first start up, the 1-2 shift seem OK but, just a tiny bit(and I mean tiny bit, 1/4 throttle) of throttle tip-in and it acts like I mentioned.
I can't even remember anymore just how many times the ATF has been changed(close to annually, drain/refill only). So that would be about 7 or 8 times. Mostly T-IV but, I have used Mobil 1 and just recently, Castrol IMV at 66,000 miles. I think it's the transmission! And yeah, that's right, only 66K. The only reason that the ATF has been changed so many times is because all of the claims of transmission failure. I can't even beleive that the transmission screen/filter is filed/dirty/blocked, although I have never dropped the ATF pan. Maybe I should.
I change the oil/filter 2X/year(about every 3K + for the same reason), Sludging! Using only oils(syn/dino, mix my own)held in high reguard here at BITOG. Generaly Purolator filters, sometimes WIX/NAPA.