Easy way to check if it's vapor lock is to pour cold water onto the mechanical fuel pump to cool it down, then retry. If it starts right back up when ordinarily it wouldn't start up, then it's vapor lock.

An easy way to bypass further problems with vapor lock on these trucks is to install an in-line electric fuel pump down low by the tank. Some folks remove the mechanical pump altogether and use electric only. My truck has both electric and mechanical (perhaps one of these days I'll get around to removing the mechanical pump). I haven't had vapor lock since I installed the electric pump a few years ago. Prior to installing the electric, vapor locks at high altitude were common. Now I can go to over 14,000 feet (I live near Pike's Peak) and it won't vapor lock.