New Guy W/trans. Level Question.

[Blind Faith]

Greetings, New guy here. Just bought a 99 RX300 for my wife and we both think the car is great. I would feel alot better if I hadn't read all of the trans/engine problems that seem common in this year and model. Not sure I would have bought it if I had known. It thought Lexus and I said, "What could possibly go wrong?". Anyway, I just changed the trans fluid and filter per the advice given here. Everyone says that 4.1 quarts of fluid will have to be refilled. I had a good 5 quarts in my drain pan and replaced that amount. After driving it and getting it up to operating temp, I was still just shy of the bottom notch on the HOT level. Is this common?. Any advise you can give would be appreciated. Thanks in advance, Blind Faith