1995 transmission slipping

I have a 1995 park avenue with 105,000 miles on it. I drove it home and parked it in the driveway and it ran fine. Several hours later my wife tried to back out of the driveway and there was no reverse. I tried several minutes later and it ran normal. This morning it would not hardly go forward or backwards. I am I able to do anything to save it without replacing the transmission? Any suggestions on what to check.

Was the car parked several hours outside with less than 45 deg temp?

No the car was in the garage last night and the temp was in the 50's.

If it is full it is coming out.

The transmission oil is full and does not smell burnt. I backed it out of the garage and the transmision barely moved the car. I let it sit and idle for about 15 minutes. I went to move back into the garage and the transmission worked like normal. I dove it around the block and the acceleration appeared normal. I had my neighbor who is a mechanic scan for any codes and nothing showd up. Thanks for the replies.