that's correct about fuel volatility nowadays. i have a similar combo- 496 in an a body, street/strip. it runs 7.0 at 3500 feet in blazing desert heat. stock fuel tank, carter mechanical pump, 3/8 line, and no fuel delivery problems at all. as a matter of fact, it had no problems with the 5/16 line either! i suspect you've got a problem possibly with your pickup, or with your system configuration. have you tried running both pumps? what kind of filter arrangement do you have?