2000 Grand AM Surges at speed

This is a 2000 Grand AM with 2.4L 4 cyclinder automatic OD tranny

If you give it the gas and let it shift thru the gears it seems fine, When you let up on the gas just to maintain speed say 60mph the car surges 300 rpms and back down then back up and back down:confused: .

I moved the shifter to 3rd and it did the same thing but to lesser degree. When I turn on the AC it seems to do not do it unless you give it just a little more gas.

Can there be a vacume leak or what ever detects the load and it trying to get it to go back to 3rd gear?

Can the trans filter be clogged and starving the tranny of fluid?

This is my daughters car and she bought it just a little while back. so I have no history.

Thanks
Tim

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