I'm a UPS Driver and have been diagnosed with epilepsy, now I can not pass a DOT physical. Ups is going to put me backpart time. Is there a case?

Hard to tell for sure, but likely not.  If you are in a DOT covered position, and need DOT clearance to perform that position, UPS is not required to keep you in that position. There is no law that requires an employer to employee anyone full-time meaning the employer can effectively change anyone from full-time to part-time and back whenever it wants.