What he said, but I would add: what's your cadence as you climb these hills? I can't relate the gear inch figure with what that ride would actually look like. If that's easy enough of a gear for that slope that you're spinning in the 80s or higher it would be very different from if you're doing like 60rpm and just burning your muscles out. Also something that training can improve, but if your normal "easy speeds on level ground" rides don't demand a lot of power-per-stroke of your pedaling, and now you're trying to mash your way up this hill, then you're using your muscles much harder than your used to. Training will help that, of course, but so will spinning faster so you're shifting more of the burden from your leg muscles to your cardiovascular system.