Throttle body or transmission?

I have a 2006 Ford Five Hundred with 139,000 miles
on it and SOMETIMES while going 55MPH on a flat
road my RPM’s will be at 2500. I can hit the gas
pedal and get the car up to 80 and let the car ease
back down to 55 and the RPM’s will at 1500 RPM’s.
A couple of days ago I took the throttle body off
and used SeaFoam Throttle Body Cleaner and used
a old tooth brush to clean it. I then wiped it down
and put it back on. It did look like the throttle body
might be getting stuck sometimes because the
plate was 2 cm back and you could see a dirt ring
and the plate wasn’t coming to that dirt right. Kinda
like the plate was supposed to be were that dirt ring
was. No high RPM’s while idle even before or after
cleaning it. Sooooo I can be driving and the RPM’s
be at 2500 and I can shift the car into neutral and
the RPM’s will jump higher and then I put it back in
drive while coasting and the RPM’s will go to 1500.
By the way, this car has a CVT transmission. Can
someone please give some kind of idea what might
be going on? It’s driving me nuts trying to figure it
out.