[JHaleyH374]

Dont rule out the poss. that your bypass is wrong either...

That's true too.....are your fuel lines long enough where you can switch the supply and return to the pump? I've never ran an electric pump, but I've always heard you want the return bigger than the supply. EDIT: Nevermind I don't see a mention of a return style setup. Maybe try a bigger vent as stated too.

 

[MadMonte]

Liquid filled gauge is my bet. Change that and I bet you'll find your problem.

I had a liquid gauge under the cowl and it would drop when it got hot also. What I found out was it would automatically change based on barometric pressure. I changed it out to a non liquid gauge and problem was solved.