I have a 2005 5.3l codes P0171 P0300 and P0455 i change the fuel pump/filter/regulator truxk

Question

Truck runs fine just have those codes it stalled one time rough idle it had high fuel pressure so I replaced those parts still no change in codes also it tells me to tighten my fuel cap sometimes

Answer 1

P0171 Fuel trim lean Bank 1

P0300 Random misfire

P0455 EVAP system Leak detected

With a lean condition , P0455 can also be caused when the purge solenoid stick open , this would cause a lean code and EVAP code, This is a popular problem for  Chevy, replace the purge solenoid. , for a P0455 and a lean code condition, But very rare it would cause a misfire condition, it can contribute to a misfire condition,