Three quick observations. One, your weight is working against you more on the climbs than on the flat. Check the weight of some of the guys that are out-climbing you and I'll bet they weigh a lot less. Second, one of the major differences in long climbs is the constancy of the intensity vs. riding in a group on the flat. Third, I wouldn't be able to climb worth a damn if I was running your gears, because I'm a spinner and my climbing really suffers when my cadence gets below ~70.
So, what can you do? One, lose some weight. I'm planning to lose 10 lbs myself, in part because I don't want to drag my 175 lbs up hills. Two, do some long climb intervals to get accustomed to the constancy of intensity. Three, give some thought to your gearing. I don't know what your "cadence of choice" is, but it's possible that you don't do as well at the cadences you are now climbing at. I'm in the process of re-gearing for a 17.5 mile hillclimb TT because with my current gearing (39/52; 13-26) my cadence drops below 70 in the steepest sections and my climbing power suffers at that cadence.