Leaving on a trip Monday Morning with my new Duramax. After reading some of the posts on this forum about low levels of rear end oil from the factory I decided to check mine. Sure enough it is about 1inch below where it is supposed to be. Dealers not open tomorrow so should I just run it like that or I can get Mobile 1 at th parts store. Will It hurt to mix the factory oil with Mobile 1 ?

I wouldn't be too concerned as its supposed to be .4~.6" below the hole anyway. My take is they put in 4qts for the initial fill and some has since migrated to the axel tubes and hubs.

I agree with ShumDit. If you're really concerned about it though, why not get to the dealer first thing Monday morning and have them fill it to the bottom of the filler hole (spec. is 0" to 1/2" below). Mine was two quarts low for the first 850 miles and was about 3" below filler hole.

Add the quart of M1 75-90wt., it's only gonna cost you about $9.00. A new rear axle?

I'd just top it off with mobil 1 and then drain it when you return. I changed mine with mobil 1 at a thousand miles. It was 2 qts low straight from the factory. I'm very glad I changed it. I plan on doing it again at 10k, which wont be long.