3-2 Nap Transition causing shorter daytime naps?

supercam705

We just dropped our 7 month old son's 3rd "catnap", but now his 2 naps that we've kept seem to be getting cut short. He used to give a good solid 1.5 hours to 2 hours each nap. Sometimes without making a peep! Now he's waking up 40 min- 1 hour in? What gives? He's sleeping 11 hours at night - which is great - but he still needs those 3 hours during the day so I am not sure what's going on. Any suggestions??