I think i'm going to swap out the manifold and look for a place that sells decent gas........ the vapor lock theory sounds familiar... i used to live in Tucson AZ and had a stock 67 383hp and drove it for about 3 yrs(before I wrecked it ) and I honestly opened the hood about a dozen times (too interested in the girls back then ).... they had regular leaded pump gas at every station and NEVER had a heating issue.