1997 automatic trans slipping

The transmision has just strarted to slip. It was first noticed while I was parked, with the engine running, on a steep grade. I checked the fluid level (while it was running, and on level ground) and it was fine. At first I thought that it might have been due to the steep incline. Since then it has become more frequent, regardless of the attitude. The vehicle has never been used for towing, and it now has 80,000 miles. At around 65,000 miles I had the vehicle serviced, which included a fluid change of the transmision. Again I checked the level and the condition of the fluid, which all seems fine. Where should I look next?

Thanks

Did they use Chrysler/Mopar brand ATF+3?

Also, are you checking the level with the transmission in "Neutral", engine running? I don't think it pumps in "Park".

I don't know what type of fluid was used...

And I'm going to go out and check the fluid level right now with it in parked in neutral...

Thanks... I wasn't checking the level in the neutral position. All is well now!

JM