I have no idea what you paid for the bike vs. what components are on it.
But if you're huffing & puffing going up a hill, but your legs are fine - it means your legs are stronger than your aerobic fitness.
My legs never actually get tired on hills - but cardiovascularly/aerobically - I need to get in shape. Now, if i don't push myself, I can get up the hills with a lot less huffing & puffing.
The road bike is probably allowing you to work yourself a little bit harder than the hybrid was...