It sounds to me as if you are already on the way to making your new ride work for you. Fitness questions aside, I think good DF riders can encounter especially difficult transitions.

Perhaps you have already found that the best way to get a good start is to choose a decent gear for the situation (that's only rarely your lowest), totally relax, and fully commit. Struggling just leads to more struggling. I had to make relaxation before starting a requirement until it became automatic.