Did a road bike rental the other week to see what I thought, pretty much loved it, then took a couple bikes out for a test run today trying to decide what to buy.

In any event, I noticed two things when I ride the road bike vs the MTB (what I've ridden all my life):

1)When riding on the road bike I feel like my power output is noticeably lower. I just don't feel as strong as when I'm on the MTB. Can differences in fit/riding position significantly impact that...or is this just in my head
2)When riding the road bike I don't feel like I breathe quite as well, and when I start to bring up the intensity I find I start getting very uncomfortable. Obviously, its going to hurt, that's part of the game running/cycling etc. but I'm talking about just a general discomfort that saps me of all desire to really hurt. My guess is that it's just the difference in feel between the more bent over position of hoods/drops vs being upright for MTB/running making my breathing feel constricted. Anybody else had this, and is it something that will go away as I adjust to the new riding position?

Thanks!