Over revving and surging

I have a 97 rodeo with 205K.
This occurance has happened once before, but seemed to fix itself. It happened again yesterday, dont know what it will do today.
Heres what happens;
Driving down the highway with the cruise control on, approach an incline (hill). Starting up the hill, the cruise works at keeping the same speed. Suddenly however the engine starts over revving, under revving and so on and naturally the tranny is trying to keep up with this. Not a good feeling. I take the cruise off and feather the gas pedal to smooth things out. Once I am back in town driving, from a stop, I accelerate and the same thing happens. The tach jumps up about 500 RPM and then back down again, over and over. My speed slowly increases, but can't stay constant on the pedal to accelerate.
The first time this after happened, I after the fact changed the fuel filter, but it had already stopped doing this "thing".
I haven't got a clue!
I read through the forum until about page 58 and wasn't finding this occurance per se.
My Rodeo has never had any major problems. It keeps on plugging away and I love it.
Thanks, pjs

Low on tranny fluid?

torque convertor?