After 45 minutes of driving my transmission changes rough

These transmissions were known for having PCS(Pressure Control Solenoid) problems with the higher miles I would agree on a complete trans flush and filter change.The Pressure control solenoid sarts to hangup causing high pressure when not commanded which will cause hard shifts.

One thing I have to say, any-ones get close to 100k on domestic transmission 4 and 6 cylinder got their money worth. Life expectancy on domestic 4 and 6 cylinders transmission usually my opinion its about 60k to 75k miles although I have seen some with good luck 100 to 150+ but rear on domestic cars. I would take it to a GM dealer and have them do a transmission flush and change transmission filter, that should solve some of your problems. If you a second owner 99% of the time no one have change fluid or filter. If you the original owner than you know its time to take it in and get it service. having nearly 100k mile pay close attention to it, change your oil every 3k miles and don't ride it hard, all the seals is old from your transmission to the rear main seals. Once a month fill it up with 93 octane and mix a can of fuel injectors cleaners keeping problems free with your injectors and your valves. Hope that help some

change the fluid and filter and add some trans x

TIME FOR TRANSMISSION FLUID AND FILTER CHANGE.