OK, I give up, so just how DOES the fuel system work? 
Don’t feel bad, the fuel delivery system and the gauge system is “unique” to the coach, that’s saying it nicely. Actually, the fuel system is weird and does not use proper logic, if you ask me. Go to Fuel Tanks for more on this topic.
Do I really have 2 25 gallon fuel tanks?
Yes, but they act as one 44 gallon tank with a 6 gallon reserve. The tanks are tied together at the 1/4 tank level through the fill system. When your gauge shows empty, flip the fuel switch to “Aux” and you will have 6 gallons of fuel left to find a gas station. My suggestion is don’t run the tank that low, its hard to push one of these babies to the next exit!
How do I know without a fuel gauge that I’m getting low on fuel?
A standard GMC floor plan coach (not a coachman, Midas, Avion, Norris, etc. pulls fuel to the generator at the 1/4 mark on the tank. If your generator shuts down while you are driving, you may want to get some fuel because you are at 1/4 tank when the generator shuts off.
Oil additive Information
Listen, I used to think all of these oil additives were an optional thing, you know — they put some magic potion in an engine then empty out the oil, pour dirty in and rev the motor up to 4K and leave it there— some gorilla tries to hold on to a screwdriver and stuff like that. Come on man, I’m not gonna piss off a primate til he sucks the oil out of my motor then spits mub back in then I need to make a fast getaway all in first gear!! I mean what does all of that really mean to me– right? Hey, there is a minimum standard to all oils and that’s enough to keep my motor safe—– right? Well, I hate to burst your bubble, but mine was and now I know different. If you already know about this, you can read on but if this sounds new to you, this is an extremely important issue– maybe even one that even though you think you know all about it you may want to read. Go to New oil formulations and don’t blame me if you didn’t know anything about this!