So sometimes my '01 1500 318 will blow hot through dash, then get cold, then get hot again, then cold... I can hear gurgling behind the dash quite often, but not necessarily when temperature of air changes coming through vents. Also, my temp gauge goes up quickly to like 3/4 (even when it is like 50 degrees out) and then it will drop to less than 1/2 in a matter of a few seconds, then the hot air comes out of the vents. Totally confused here. Have checked MANY posts, but none describe this issue that I have seen, so sorry if it is a duplicate.