my Trans has been acting up lately in that it seems to run fine for about ten minuets at cruising speed but if I speed up or slowdown then go back to cruising speed it no longer goes in to overdrive but I can left off the gas and it will pop back in, its almost as if it thinks I am trying to pass even when I just have the cruise control on, any ideas as to what it might be? this is dropping my gas mileage to... as it sticks at 3500rpms most the time now at 70mph instead of the normal 2500rpm.

When is the last time the fluid and filter has been changed?

also check you vacuum line running from the throttle body to the trans. I just replace mine because they were cracked and slit and it sured up the shifts nicely.