if everything is the same except the new crank. Read the length on the inside of each arm. You may have been given longer crank arms than you had previously. I recently went from 175 down to 172.5 and that made a big difference in a good way for me. The 175's were a bit stressful on my old knees. If your shoes are the same the seat is the same there isn't much else that could cause a sudden difference.