Cold Start on 99 Silverado

[Marts99Silverado]

I have a 99 Silverado with a 5.3 vortex. It’s middle of winter here. We’re getting colder than normal temps. (20s down to single digits.) couple weeks ago I realized when I would start my truck in the morning it’d be idling, and then it would bog down to under 500 rpms and sputter. Just for a brief moment then rev up to 1500 or so and do the same thing. I don’t know what is causing this. Any ideas ? I could post a video tomorrow morning and show y’all. Appreciate your time and thoughts. Thanks to all in advance. 

[Jsdirt]

A few things could. Failing fuel pump, throttle body, or wiring issues. Also stale gasoline, or gas contaminated with water, fouled plugs, or debris in the fuel system, and probably 20 other things I'm not thinking of. Have to get a scan tool on there and see what's happening when it stumbles.