9 Silverado runs ok when you slowly accel, but when you accel hard it starts to stall out. Only codethat is thrownis on IGN on P0405. No other errors and P0405 does not return after cleared until IGN turned off. Any good places to start looking. Almost acts like a hard miss. Fuel pump and I believe filter have been replaced already. changed TPS to no availe, cleaned Throttle body, EGR and MAP sensors. All appear normal. Did notice engine ran without codes with the MAP unplugged. Thought this was odd. Truck run fine when throttle is worked up, but when you hit the gas hard like passing it starts back-firing. Please help, Desperate to get fixed.