Buick Roadmaster fuel cap / fuel pump

From my grandma who can’t figure out this crazy problem:

I drive a beautiful 1994 Buick Roadmaster. Runs and rides like a dream. 113,000 miles and doesn’t use a drop of oil. I replaced the fuel pump last May and shortly thereafter on a hot day I cannot not start my car until I remove or loosen the fuel cap. It sounds like opening a large bottle of soda. Replacing the fuel cap did not help. My mechanic is stumped! Is there a connection between the fuel pump and my problem? Help!

It sounds like the evaporative emission system was messed up when the fuel pump was replaced. Maybe they kinked or pinched the vent hose?