2003 7.8 loss of power

[riverrat]

Hi Brand new to your forum hope you can help.I have an 2003 C-6500 Chevy. It has about 115000 miles on it. I got it 86000 on it. It always has been hard to start only when it has been sitting more then 5 days or so. No fuel leaks serviced every 6000 miles with oil change and fuel filter. Lately it has loss of power not at take off but after 65 miles per hour. It has Duel 45 gal. fuel tanks on it that draw independent and when we fill them up the drivers side tank always needs about 15 gal. more than passenger side. Is there lifter pumps in the tanks or maybe a valve where they come together? No check lights on. Thanks for your help It has 7.8 Durmax