Start with a cold engine. Remove the radiator cap. Start the engine, and let it warm up. Having the truck parked facing uphill sometimes helps too..... when the thermostat cycles, first it will push coolant OUT of the fill....... then it will suck it back down. There is a neat tool for this, that is basically a funnel that attaches to the radiator neck, so you aren't blowing coolant everywhere....... when the funnel gets on toward empty, add some more........ let the thermostat cycle several times, and it 'should' get all the air out.