Sierra Start up Problem hesitates sometimes 2004 Sierra

[Mike Organ]

So every now and then my truck starts funny. Maybe once a day.    I have done a recent oil change.  Plugs and wires look new. I took one plug out it looked good. Tapped on the starter. I took the throttle body off and cleaned it with TB Cleaner.  

 

The battery is older. It has no fuel filter installed(yet) .  Soon as it starts it runs fine. Just sometimes hesitates at start up. Always starts tho. 

 

Truck is starting to knock slightly and just last week I got a code for knock sensor but had the starting problem for a while. 

 

Please help.