These problems should both be in the 4T65E section for future referrence.
-Smokinum you could have a number of problems and when shift solenoids fail on these cars there will generally be a code in the history for electrical or mechanical solenoid failure. You really should have an experienced transmission diag guy drive your car with a scanner and see what is going on to verify proper operation and find out what is causing your problem. These transmissions are completely electronic / pcm controlled so a number of circumstances will case the transmission not to work properly such as engine sensors not working right.
-SilverMist01 your problem sounds like a failing pressure control solenoid and is very very common on these transmissions. The harsh shifts and loud whining is the result of the pcm commanding max line pressure to cover up your problem and is a failsafe to keep the trans from burning up. If you check your codes you will likely have a P1811 in the history. This code will not turn on the SES light and will reset with a key cycle and the car will drive normal a short period of time again just as you say.
