Usually it's not that trivial. First try changing the fluid. And make sure the level is proper. If does not help most likely you will have to change transmission.
Bearing needs to be replaced
No oil pressure
Have it looked at by a professional transmission specialist.
Timing chain usually needs to be replaced each 180-200K miles.
Transmission needs an overhaul
Your High/Low switch is bad and needs to be replaced.
Sounds like your heater core needs to be replaced.
A 1999 Toyota Camry needs four quarts of oil :-)
how do you check to know whether your coolant fan motor needs replacing in my 1993 toyota camry v6?
How do you know if it needs to be replaced
I was told that it is the temp sensor. The car needs to be at 150 degrees. I am working on the same problem.
In general, engine thermostats can be found by following the LOWER radiator hose to where it attaches to the engine. The hose is typically attached to a fitting behind which is a gasket and the thermostat. The gasket needs to be replaced when the thermostat is replaced.