Your problem is related to the skimmer basket - having it AND the vac adapter in there REALLY reduces flow, remove the basket and just let the big stuff catch in the pump basket - works like a charm - the only time you have to shut off is when you've lost so much pressure due to dirt collected that you have to backwash - at which time you can close your valves, empty the pump basket, open the valves again, prime and then go through a backwash/rince cycle.
Also, if your water level is pretty low (just above skimmer) it's even easier for air to get sucked in around the adapter, always make sure your adapter seals well, even though it sits in there good, sometimes you get more leakage than other times