Hope someone can help I have a 99 silverado 4.8 when cold has power loss and sounds like its backfiring till it warms up after it warms up its seems to be ok till I shut it off for even 5 or 10 minutes and it will do the same thing loss of power and a muffled backfire, any ideas

 

codes read so far?????

 

Yeah I guess I should have put in my post the truck don't want to give up any codes at this point anyway