Stalls after an hour driving in summer months on 1990 Jaguar Vanden Plas

The car will stall out after an hour of driving if the temperature is above 85 degrees. doesn't happen on cooler days. After about 2 hours, it will start again.
My suspicion is vapor lock from a weak fuel pump.

Vapor lock occurs when the engine is hot and you turn it off, then try to restart it after several minutes. It doesn't occur while your driving. This sounds more like an electrical relay is getting hot an failing, fuel pump is failing or a control module issue, so pretty much anything electrical can cause this type of problem.
The ideal thing to do is verify the problem and perform a "no-start" diagnosis when it occurs.