You've got it backwards. Lower gear you spin the pedals easier, high gear requires more effort. You should be spinning the pedals at a fairly steady cadence. Use whatever gear it takes to keep that cadence. If that means the granny ring moving 3mph uphill, then fine. In the beginning, think of the front chainrings as ranges, and use the back to fine tune. Try using the middle ring on the front on level ground, the small ring uphill and the big ring downhill. Once you are stronger you will spend most of your time probably in the middle and big rings, but don't try to get there too early, keep the pedals spinning at least 60rpm. 80 or 90rpm is better, but will take some conditioning to get there.