Car revs when in motion, not when idle.?

Question

I can be driving down the road, usually low speeds (but once at high way speeds) after the car has been on for a while (I.e. not in the morning when I just start the car up for the day) and the car will just start reving up and down about 500 rpm or so when I have even pressure on the gas. It doens't do it when I'm idle. The check engine light is not on and the last time I took it in the mechanics couldn't find any "codes" on their little computers. What is going on here?!

Answer 1

my answer is try to check it out first on auto repair shop..

Answer 2

your transmission is slipping.  pretty expensive fix 2-3k.  when your transmission slips the gears are slipping past each other causing your engine to rev higher but your car to remain static