sorry for your loss, but i'd have to agree with del
was the water in the 55 the same water that was in the 75 before the move?
was the 55 aerated?
did you put the old water back in the 75 or use new water, if so how much and what temp difference?
did you keep filter media in moving water and not just let it stop flowing for a while?
things like this need to be considered, people move fish across states and countries just fine, large fish like yours should be able to withstand a lot but need lots of air, sorry to point out these things after the fact