2001 GMC starting problems

has the 5.3 engine, if it sits awhile (overnight) is hard to start. if it sits a little while easier to start. have changed out the following; fuel pressure regulator, vacuum line for regulator, new plugs, wires, fuel filter. dealer "fixed" fuel sending unit due to faulty readings on fuel gauge. Fuel guage works fine now, but still hard to start

Welcome to AF. What is the fuel press, key on, no start, basic diagnostic step for this condition.