So here's the deal, if I start my truck warm it up for a couple minutes drive to a stop sign then let it idle it pulsates up and down. Then when I drive it for some time it stops but then idles super low at like 500rpm, yes under 1,000. I've had my buddy look at it and use a no drip funnel to get rid of a lot of air bubbles In the coolant, but it did it again. We thought it was the head gasket but there are no signs. At one point it got way too hot and the heater was cold which points to air bubbles and we got rid of a ton. We couldn't see any gaps where air could come in. When the funnel was in the radiator it idles to about 1500 filled the funnel with coolant then bubbled a bunch and sucked it back in then idled perfect. and when i drive it on the road it does the same thing but dumps coolant out of the overflow then getd hot Because theres no coolant. Does anyone know what the problem could be? This is a brand new motor with 6,000 miles on it