The van is not going to Back from the Dead- Bob Goodwin 30 years exp. factory trained is working on her. He says there is nothing wrong with her. He is the one who replaced the head gaskets and put NEW heads on last May. I have driven about 18,000 miles since then- entire cooling system has been replaced including radiator. Still getting air. he is not driving the van on the freeway which is the only place that I have a problem. It was actually fixed for awhile but have been battling this problem for a couple of months now. Thought the problems came back cause of  a leaky radiator, but replaced it & still getting air / only on extended high speed  over 60 for 30 minutes or so especially if in the mountains. But NOT OVERHEATING, if it were the head or head gasket wouldn't it overheat.  Any cooling gurus out there with any insight?

Michael