2003 Pontiac Montana starting

When I start 2003 Montana the engine cuts out, doesn't stall, before I can get my fingers off the key, turn the key again and it starts and runs fine. This happens EVERY time, hot or cold. Have plenty of fuel pressure, put injector cleaner in tank, had injecters cleaned at oil change place, turn key on to let pressure build up, then start, still happens.
About every other day the knock sensor code comes up, replaced knock sensor code still comes up about every other day. Battery is original but still says 12.5V.

thanks
PK