Nissan Altima 2.5s

Originally I changed the starter, pcv valve, air filter, oil chane and filter, spark plugs, battery, crank sensor, thermostat, then the head gasket, oil change and filter again, valve cover gasket, but the car still has smoke out the exhaust. Wshite smoke. Thick doesn't go away fast. Not continuously sometimes only when I hit the gas. But along w. The smoke comes this stutter thing. Like feels like it wants to stall out but doesn't. I can not and do not know what to do next w. This car and thought I should get some advice? Btw does not over heat. Rpms a little higher than normal though.