Service transmison lights coming on

i have a 04 century with a super 10. it was remaned last june by eaton-fuller. for some reason after a 30mile ride,the red service transmission light comes on and the truck slip gears and stop shifting. The truck has been at freightline for 2 weeks now and theyve put a harness somewhere.They drove the truck for 10 minutes,i told them to drive it for 30 miles. Thy did and it happened to them also. Has anyone ever had this problem and if so, what was the solution? thanks