454 just dies.

[C30Seenemall]

I am Baffled, Puzzled and Flabbergasted, otherwise known as Wayne.
My mechanic and I have been trying to figure out why the 454 in my C30 Scottsdale Camper Special keeps dying.
The problem?
Each time I drive the truck a total of 26-29 miles, the engine sputters then dies. I can pull off the road (not easily with no power steering) put it in park and it fires up easily. If I continue to drive it will go about 1 or 2 miles then quit again.
The mechanic and I think it is vapor locking but we aren't sure why. The previous owner put an electric fuel pump that seems to work fine but they installed rubber fuel lines. The mech found the lines were about 1 inch from the exhaust pipe! He subsequently moved it about 4-5 inches from said hot pipe.

But the engine is still dying on me.
My opinion is the fuel lines should always be steel instead of rubber under the truck. Am I correct in thinking that?