Does the "service engine soon" light come on? If not, the problem is something GM didn't consider. The fuel (injector) pump shouldn't be causing this unless you have purchased contaminated fuel and your fuel filter failed. This is the reason for injector failures on certain years of trucks. Diesel fuel has a natural affinity for water, and condensation in the empty part of your fuel tank will accumulate a surprising amount of water in your tank, especially when the outside temperature swings large amounts from days to nights. The flexible fuel lines deteriorate from the inside out, so when it's noticeable, the inside is really bad. The lining may swell and block fuel passage, suck in air without leaking fuel out, or simply reduce the amount of fuel flowing. If your truck is over 3 years old it's worth an inspection because of your complaint. I'm only an amateur so don't take my advice as gospel.