[Travis1974]

This may be coming WAY out of left field but here is what happened to me.
When I first built my 72' it had a crate engine. I drove it most of the summer in central Texas and fought overheating. Especially if I was sitting at a light. It ws boiling the gas in the fuel filter and vapor locking too. I went round and round with the cooling system and heat shielding all the lines. The works. No help.
Then one day I had to pull over in traffic to let it cool down and this good ole boy pulled over to help. I told him all about it and he said "its your timing". What? no way. I am dialed in exactly to factory specs. checked it 3 times. He said "trust me, I do nothing but build old chevy engines on these old trucks. The timing is for 1972 gas. You are running 2014 gas. You need to advance the timing 10 degrees." "trust me". I had nothing to lose and went home that night and advanced the timing like he said.
2 years later she still runs PERFECT. dead center temp even in 100 degree temps and in traffic.
Try it if all else fails