Hello Allie1823,
According to Stanton's WWII Order of Battle the 2756th Engineer Combat Battalion was originally the 2nd Battalion of the 591st Engineer Boat Regiment. The reason for the new designation later on I do not know. The book provides us an outline of their movements.
591st Engineer Boat Regiment
15 JUNE 1942 Activated at Camp Edwards Mass
5 AUG 1942 Departed New York P/E
17 AUG 1942 Arrived in England
2 NOV 1942 Departed England
8 NOV 1942 Assaulted Oran (Operation Torch)
6 DEC 1943 Arrived in Italy
1 NOV 1944 Deactivated with assests to 1185th Engineer Group
Campaigns: Algeria-French Morocco, Tunisia, Naples-Foggia, Rome-Arno, North Appennies
2756th Engineer Combat Battalion
10 OCT 1944 Formed in Qualiano Italy from the 2nd Battalion, 591st Engineer Boat Regiment
20 DEC 1944 Arrived in France-ETO
AUG 1945 location; St. Martin Czechoslovakia
25 JUNE 1946 Deactivated in France
Hope this helps you a little, good luck with your search. I also found a thread on another forum that had been discussing the 2756th, and has many photos you probably will what to check out, click on the link below.