87 dakota vapour lock

I have a 87 dakota that is suffering vapout lock. If I drive it for 15 min in the heat and let it sit for about 5 min, I have to crank it for a long time before it will fire. If I drive for about an hour on the highway it just dies. If I let it sit for a half hour is good for another hour. The fuel sock, pump, and filter are all new. The o2 sensor is new. The carb has a thick gasket and one inch spacer under it that I believe are to help keep the carb cool. The belt was also off the air pump. Any ideas would be apreciated. Also I would like to know if disconecting the air pump hurts gas milage. Thanks.