1997 Bonneville problem

my 97 bonne has a problem. drives fine for a little while ( a mile ) then ill be going along and then the rpms go up and the speed doesnt. then i have to stop and wait then start it back up and i can go for like 100 feet then it does the same thing. hoping its not the transmission and maybe its a sensor? the check engine light is on so i bought a Actron OBD ll Autoscanner. i hooked it up to the car and scanned it and it said there were no errors. the check engine light is on so i dont know why it would have no errors...? well if anyone might know what this might be.. let me know. thanks Jeremy

another thing... when the car is off ( with key turned to accesory position ) the check engine light is on. then when i start the car it turns off....????

Unfortunately this does sound like a transmission failure. However, since the transmission is controlled by the PCM you may have a problem with the PCM or wiring to the transmission from the PCM. If the CEL is on then there must be an issue somewhere and the scanner should pick it up especially if it relates to the engine or transmission. Take the car to a tranny shop and get it scanned with a trans capable scanner to see what is actually going on.