Is 20-25 psi normal for an idling Chevy Vortec V-8 5.7 liter engine? It sounds fine and it goes up with RPM.?

yes its fine its not so much the pressure as much as having it instantly, oil pressure is dictated by clearances in the motor but as long as the guage goes up when you start the truck youll be fine especially because those guages are very inaccurate. when it starts dropping below that you have a problem internally in the motor