2000 Chevy Truck entended crank

My Chevy 2500 HD Classic body style 4x4 with a 5.7 l. V8 has a very long crank time. Fuel pump died 18 months ago, I replaced it and the filter. Truck started great until a couple months ago. Crank time has grown longer and longer over the past couple months. I live in Michigan and the temp has gottten much cooler over the last couple months. I can hear the fuel pump running and stoping like it is suposed to. I cahanged cap and rotor, all plugs, and wires last week, no better on start. Changed crank sensor today, still have problem.