overheating and misfiring

so today while i was going to work i noticed the truck was misfiring so i pulled over checked the oil and it wasnt even registering on the dipstick, 3 quarts later the oil was good but it was still misfiring so i figured it was a bad coil and decided i would deal with it after work. then about 5 miles down the road it started overheating so i pulled over again and the radiator was out of water so i filled that up. I made it to work but on the way back, it did it again so i pulled over and the radiator was dry again so then i started thinking head gasket, so i checked the oil but it was fine, not low good color and good consistency (not milky) but when i opened up the oil fill cap there was a thick milky residue on cap. so ime kind of thinking head gasket but i dont see why all the oil wasnt milky. anyone have any thoughts? thanks in advance!! Oh yeah when i ran the codes it was a multiple misfire