So my 1984 C-20 350 W- 700R4 has the semi floating rear axle and I'm looking to swap it to the full floater we are talking the factory full floating diff, not some other diff. I believe that it is very likely the current axle is 3.08 unit, but I've not removed the cover to count. RPO code indicates that it is the "standard axle" with no reference to axle ratio, and really I should and will find out my true axle ratio before proceeding. My main questions, I "think" that the axle housing is the same size so I "think" I won't need to shorten my drive line, but I could be wrong, if someone knows that info that would be great. I know some of you are going to get whinny about this, but fuel economy is a concern, for me. Look I know most of these trucks aren't mileage makers, but I don't want mine to be any lower than it is. I spend a good amount of time loaded, but also have some long freeway drives to get some of those loads. One of my concerns is that most of the stock full floating diffs I've seen seem to typically have axle ratio of 3.73 or 4.10 I'm thinking if I look for one with a 3.73 ratio that should be ok, with the 4.10 probably being a bit lower than I'd want to go, really I'm just looking for a second opinion / other thoughts from ya'll.