Misfire and headlight dimming

2007 Tahoe LTZ, 4L60, 4x4, 311,000 miles.
A week ago I noticed upon hard acceleration that there was something amiss, I could feel the engine misfire. Then 2 days ago the engine would misfire pretty bad at a cold startup, but it went mostly away as it warmed up. I thought I got some bad gas, talked to a mechanic friend and he suggested resetting my Ethanol sensor, and sure enough it was reading high, this helped a little, but still getting random misfires.
I plugged in my tech 2 and it was misfiring occasionlly on 3-4-5-6-7 but mostly 7. I pulled the plug on 7, it looked fine, color was good, not oily, but the *** was missing on the plug which was only 50,000 miles old. I had an old plug that looked better, so I put that in, and it ran a little better.
What I noticed tonight was the headlights, and interior lights dim every time I get a misfire. Which seems odd to me.
Wondering if anyone has run into this, I thought maybe a bad ground, I have no SES light, no engine codes at all.
I am going to try replacing plugs and wires to see if it helps, but because the lights dim I am wondering if I sould look elsewhere too.

Disconnect battery, slow charge overnight and have a shop load test it. Replace if needed. If not …

Time to replace your -/+ battery cables. They rot from inside out but still look perfect.

You also need to verify your fuel pressure off the tap on the fuel rail. If subpar only replace w/ OEM ac Delco - GM unit from R/A - about 2-$2.5h.

I replaced spark plugs and wires 1-7, I can never do 8, so I pay someone to do it for me. I was not getting a misfire on 8, however if I continue to get a misfire I will be getting new battery cables, I appreciate the input on that. I have a friend who I asked about my issue and he said the exact same thing and there is a TSB on specifically the positive cable, and there should not be more than a .2v variance between the battery and. The where it connects to the starter.. So that will be next. Thank you for taking your time to reply.

I ordered new Battery cables, hoping to do both of those this weekend.