Would there be a significant mileage improvement (enough to justify the expense) in my 1997 Chevy Silverado extended cab 4X4 w/ Vortec 5.7 gas V8 if I install "Warn" type hubs on the front axles? Or is it even possible? I am currently getting 13.2 around town, 99% pavement driving.
I used to have a Dodge 4WD pickup with manual locking hubs on the front axle. I didn't run extensive testing, but on those occasions when I did check I could measure no difference in fuel mileage with the hubs locked or unlocked. Leaving them locked kept the front axle oil seals from drying out and made use of 4WD much easier, because I didn't have to get out and lock the hubs.
I don't know about the gas engines, but with the Dodge Cummins diesel truck, people are seeing between .5 and 1.5 mpg gains. Yes, they are a pain to install, they are expensive but you get added fuel economy and they are cheaper to rebuild than replace worn out hubs. With that said, you can replace quite a few hubs for the cost of a spin free hub assembly.