Your grandfather was a member of Company I, which made up part of the 3rd Batallion of the 30th Infantry Division, which in turn made up part of 3rd Infantry Division.
the 3rd Division had a long and illustrious career during WW2, arriving in November 1942, fighting in Northern Africa, Sicily, Italy, Southern France, and finally ending up in Austria at the end of the war in May 1945.
They remained as occupying troops in Austria, until they returned home in September 1946.
The RA with the serial number shows your grandfather was "Regular Army".His serial number shows he enlisted on his own, and was not a draftee. (Draftee serial numbers begin with a 3, usually.)
Considering he was in Germany over a year after the war ended, I'm guessing he probably joined the unit late in the war.After hostilities ended in May 1945, men were shipped home on a "points" system... you got more points for the more battles you were in, medals you won, dependants you had, etc.High point guys went home first. If your grandfather was there for over a year after the war ended he probably didn't have enough points to get sent home right away.