I have a '98 K1500 Silverado I got after my father passed. So I don't know much about the truck and it'* issues outside of what I have fixed and learned about it after driving it close to a year. The background I do know is it had sat for at least 5 years and that is about it. Knowing that I had changed all plugs, cables, cap and coil about a year ago. It had been running great for close to a year since then, but now I have a PO305 (misfire in cylinder 5) I hooked my diagnostic tool up and found looking at the Freeze frame data the fuel system 1&2 were in a Open Looped. I also ran it in live mood and in a 20 minute drive and the fuel system 1&2 was in a Closed Loop-fault. I was going to test a bunch of things I had found online this weekend, but I was hoping someone here may have a good idea what it is or where a good place to start testing would be.
Thanks in Advance!

I forgot to add that it only runs rough when idling. It for the most part runs great when I'm giving it the gas, but from time to time you feel the miss while driving.

What you are seeing is what fuel mode the engine is in. During warm up, the fuel system will be in open loop. Once engine is at a minimum temperature, it goes into closed loop which all sensors are being used to calculate fuel usage etc.

If you already changed plugs, wires, rotor and cap, I'm gonna lean towards the fuel spider assembly. These injectors are notorious for leaking and causing misfires. There is an upgraded fuel injector assy for these 4.3 and 5.7 engines.

Thanks, I had a feeling that was the case.