Riddle me this.. Getting ready to do 1200 miles on my 99 suburban with a NP246 auto-trac transfer case. I have the front drives shaft out now to get a u-joint replaced which got me to thinking. Would I see an increase in fuel economy if I left it out for the trip? The front output shaft spins constantly with the auto-trac transfer case, however I understand that there is no "power" being sent to the front wheels. And yes, I'm doing most of the basic tune-up stuff right now that will REALLY make a difference, including: New O2 sensors New distributor cap/rotor New air filter Oil change Seafoam throttlebody treatment A/C fixed (yea for A/C!) I can't think of any reason why I would need to have it in.