If you read the manual, it says to cycle the key 2-3 times leaving it on for 30 seconds each time (IIRC). What I did was to take the filler cap off, turn the key on, and listen for air. After the 2nd or 3rd cycle (you can hear when the fuel pump cuts off), no more air. Start truck, and it runs fine.
You have to be careful of the air getting into the pump and injectors. Air is bad for these things.
2004.5 Silver Birch Metallic GMC K2500HD
18 Denali CCSB 2500 4WD Mineral Metallic with Cocoa/Dark Sand Interior