Eaton 13 speed is acting up. As if the power gets cut on/off on/off,

I know this is an old thread but came across it trying to figure out a problem I have 98 Pete with a cat3406e 6ts 13 speed loses vehicle speed I believe is what the code meant. It only does it in hotter weather will be cruising 75 and it will start slowing down to 73 and will cut back in and speed back up to 75 that’s with cruise off and foot to floor changed out one of the sensors on tail shaft of tranny had a guy re wire sensor to ecm and still does it I even tried swapping sensors out to the other one right above it and it makes it worse only 65mph truck has no govener?????