I use to ride on a 54cm LOOK 765 road bike, and was ok while doing long rides with peloton groups, but then I switched to a 51cm BMC TeamMachine SLR01 (did fitting and adjustments), but still having a hard time keeping up from the middle of the ride to the end. Is it because of the period of getting used to a new bike? My legs give in a lot faster… no aches or pains at all with my back, knees or arms. I am 5’7 feet and 147 pounds. Any recommendations to how to getting back to normal and stronger?