2001 Gmc Yukon 2500, multiple issues (possibly related)

[Kaptain America]

as the title states its an 01 Gmc yukon 2500xl with the 6L, has approx 200K on it. So far I have replaced plugs,wires,an bad coil pack, knock sensors, intake manifold gaskets, o2 sensors,fuel filter,air filter,knock sensors,cleaned the MAF,cleaned the throttle body,cleaned the battery terminals and replaced the alternator. I have cleaned several of the grounds including the ground at the firewall, under the drivers seat, and the ground under the alternator. truck has a less than 1 yr old battery in it, had an ongoing issue with it killing the battery overnight, believed it to be a bad diode pack in the alternator, replaced the alternator and let the truck sit at my work for about 6mo. every mo or so i'd go out and fire it up and let it run for a while and every time it started no question, snow flew here the other day decided to fire it up and take it home. first night at home battery is dead, get it back running(double check its charging) and hour 3 into the trip it develops an intermittent miss, only seems to do it at idle, raising the rpm the slightest amount seems to cure it. It has not yet thrown a CEL but when it does I will add it to this. I'd also like to add when fired up from cold it runs perfect for a while, then the miss develops. when given any amount of throttle weather that's just trying to keep under 1000rpm or flooring it also clears the miss. the other issue she has is the fuel gauge will go from reading what appears to be correct to empty with the digital display warning showing low fuel then maybe 20 seconds later or when the light turns green and you go it corrects. doubt this is related but figured worth mentioning. Thank you to whoever takes the time to read this, and or give any insight.