1993 GC RPM problem

My RPM's keep fluctuating from 2000 to 2500 at highway speeds. It feels like it's dropping down a gear, which would cause the RPM's to raise, then the RMP falls back down, as if the car shifts back into a higher gear. I got a tune up and fluids changed but it didn't solve the problem. Maybe it's the vacums, but I'm not sure. If anyone has any suggestions I would really appreciate it, thanks.

My RPM's keep fluctuating from 2000 to 2500 at highway speeds. It feels like it's dropping down a gear, which would cause the RPM's to raise, then the RMP falls back down, as if the car shifts back into a higher gear. I got a tune up and fluids changed but it didn't solve the problem. Maybe it's the vacums, but I'm not sure. If anyone has any suggestions I would really appreciate it, thanks.
[COLOR=palegreen][FONT=arial black]I :banghead:

I use to have a similar problem in an older car , check your transmision oil level .

I did have the transmission fluid flushed, but I'll take a look at the oil levels, thanks.