I have a 1999 Avalon with 150k miles. Need info on transmission service and other services.

In my opinion servicing an older transmission can be a crap shoot. Hear horror stories of owners servicing them only to start having problems shortly after. Does the fluid still look good? Does the fluid smell burnt? Is it shifting properly? If your fluid looks good and it's shifting properly I would not worry about it so much. Just keep an eye on it for changes in color, smell and shifting. When you notice any changes in these I would then have it serviced.

One thing I notice with the transmission though. In the mornings, when the engine is cold, it does take a bit longer to shift in lower greats (I see the rpm going higher). However, when the engine is warmed up, it does shift quicker in the lower gears (about 10 min -- give or take a few mins). Is that normal for car of this age? I looked at the color of the transmission fluid. Its seems ok (pinkish), though i can smell *tad* burnt smell.

Yours might be on the verge of needing the fluid and filter changed if it smells that way. But if it was mine I would add some CTC to your transmission fluid. CarQuest carries this. Using this will clean the valve body and also swell all rubber seals it comes in contact with. This will in most cases clear up cold shifting issues.