2010 I get the red overheating signal at high end speeds of 80+mph. It turns off after I slow down to about 60 and won't turn on again unless I get back to 80+. The coolant has depleted slowly and I've topped it off every couple weeks. It's worse when the weather is colder. I used a coolant pressure test and it maintained pressure at 16psi. When I pushed it up to 20psi, it would slowly loose pressure. I wasn't able to see any obvious leaks. Under both circumstances, it would oscillate roughly .5psi up and down (not sure if that's normal). Thoughts on the dilemma? Head gasket issue seems to be the biggest fear.