While I was switching out spark plugs on the passenger side, I was fighting with one of the spark plug wires and after finally getting it off I noticed a long hose leading from what looked like the engine bay somewhere to about the length of the valve cover just under the spark plugs. I was in a rush to put things back together but didnt see anything that immediately looked like it was connected to and assumed maybe it was a drain for the ac?

Well after I got the plugs back in I started getting a noticeable misfire ( there was already a leaser exaggeraed one before)every so often and not sure if it was related to that or if my coils are just on their way out. Its a 6.0. I didnt think to take a picture of it but hoped someone may know what one im talking about

 

It's likely the vacuum line that goes from the top of the intake manifold to the HVAC junction then on to the vacuum reservoir ball under the battery. Take off the dog house (engine cover) and you will see it. Is it 7/32"?

https://chevroletforum.com/forum/exp...d-bolt-116653/

 

Another link with pictures. https://chevroletforum.com/forum/exp...-117027/page3/

 

That's almost certainly the hvac vacuum line as others have said. While you've got the doghouse off and you're working in that area, I would just go ahead and replace the hose. If your van has been around long enough to need plugs then if the hose isn't dry rotted and cracked by now it will be soon. When that hose goes you won't be able to control your AC vents and it will always blow through the defroster. At first it will still work when idling, but later on, it will be stuck on defrost no matter what until you fix the hose. A completely broken hose can even result in problem codes - (P0174 engine too lean, for example)

The hose is 7/32". There's also a second hose, shorter and smaller 5/32" from the check valve (the junction mentioned above) to the reservoir. I recommend that you go ahead and replace it all.