Ok. This sounds like things are working as they should, but you are just right on the edge, speed and throttle position wise, of a point where the transmission wants to unlock the torque converter to add additional RPM to sustain the speed. Now if this is happening at more than one speed/throttle position...

 

the only speed ive noticed this at is 70mph, city driving and any other speeds lower than 70 are a-ok.

 

I am actually having the same problem (or at least very similar). My transmission is doing the same thing where it will rev up to 2500 or so for a few minutes, then rev back down, and back up... you get the gist. It does this at every speed that I can hold steady between 45 and 80 MPH, but only when the transmission gets warmed up. I'm in the midst of replacing the filter (most likely won't work, I know, but for $20 or so, it can't hurt) even though the fluid looked relatively good (only a mild hint of darkening, not burnt smell). I did notice a bit of foam on the dipstick when I checked the fluid level. Suggestions?

 

Foaming transmission fluid is not good. This can cause accelerated wear on the transmission components. Foaming fluid can be caused by a low fluid level as well as a leak on the suction side of the pump allowing air to get entrained into the system. If it happens at more than one speed, then there may be a problem with the TCC solenoid in the transmission not holding properly to keep it locked in.

In the case of it happening at various speeds, there also could be a problem with the brake switch adjustment. If it is activating, it will cause the torque converter to unlock.