First off thanks for the replies I got on my oil question. I decided to try the 15-50 mobil for kicks-n-grins Also ran by my local AutoZone and scored a case of GC! Guy behind the counter said nobody was buying 'cause they were scared of the fact it was zero weight. Good for me! (I'll try it in the wife's Expedition) Anyway, my next question for the no-it-alls of oil is about trans. fluids. My truck has 80000 miles on it and has never had anything done to the trans or transfer case. I haven't had any problems with it so far and was wondering if i should leave well enough alone. At the same time it bugs me that the fluids been in there so long( call it my primal earge to tinker with stuff!) If I do decide to change it what would be the best way to go about it? I'm leary of pulling off hoses and running it like I've seen some people post. Also, what fluids would yall suggest. It's a 97 Georgia Milk Cow Z71 with towing package. Thank you for your support.