Need Help On 2002 Silverado

I Have A 2002 Silverado Extended Cab With The 4.3 Vortec. It Recently, After Shutting The Truck Off For Approx. 15minutes Or Longer Would Start Fine, But Then Stagger For 30-90 Seconds With No Power, Then Runs Fine. Had It To The Dealership, They Kept It For A Week, No Codes, Took Recordings Of The Problem, Finally Decided To Replace The Fuel Pressure Regulator And Mass Air Flow Sensor. Well, It Still Does It. Back At The Dealer For 3 Days Now, They Are Going To Replace The Fuel Pump, Claim Mine Is Working But Think It Could Be The Cause. Any Ideas Or Help Would Be Greatly Appreciated. I Really Don't Want To Get Rid Of My Truck. I Am A Chevy Guy.