Vapor Lock Parameters?

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It looks like a fuel with an RVP of 9 would have vapor pressure of 1 atm at about the temp you mentioned, so you may be correct.

So what can you do? Here is a partial list of IDEAS (no gaurantees):
1. Cool you fuel via some sort of heat exchanger
2. Run lower pressures (which will require larger injectors and/or recalibration, this suggestion is mainly if you are trying to run excessive pressures as some people have been known to do) - should reduce required pressure head for your pump, and also possible reduce heat addition from the pump to the fuel
3. Mount the pump lower - more available head
4. reduce pre-pump restrictions - same
5. Use a smaller pump - less circulation will mean less heat addition via the return line, and will also probably introduce less heat at the pump. Doublecheck you fueling requirements on this one. You could also take this to the extreme by going returnless.

I had a car with the same problem but it would lock at 100F. I tried new regulators and fuel line and it still would lock at 100F. It turned out that the Borg Warner pump that I had did not have enough head pressure to over come the tank pressure on the reticulation of fuel causing a lock while cruising. The fix for my problem was a pump with a higher head pressure. Another thing you could do it install a pressure relief valve that would vent the vapor out side the car not recommended but it would control the problem.