do you get better gas mileage if you drive in overdrive all the time?

The short answer is not necessarily. On long distance travel (constant speed and little acceleration needed) the overdrive works great and saves you a lot of money on gas. Short trips (even on the freeway/highway) or while in stop and go traffic, your savings will be greatly reduced - in some cases (although few) it can actually cost you more money to use overdrive.

Let me make sure I understand what you're saying. I drive on the high way for 40miles to work and go 70-75 the entire way, I do not stop and go. I CAN drive with my overdrive off (LIGHT ON)and it can help with gas use? My Jeep is in 4x4 all the time, in my head I feel like having overdrive on is for when I want to tow, drive in snow, mud, sand and drive around town. overdrive ON (Light off) OR AM I JUST TOTALLY BACKWARDS... Just got the jeep last week and cannot figure out which advice to go with, then I stumbled onto your post and you'res makes most sense, I have a feeling my mind has just created a HUGE block to understanding this situation.

Actually with most tow vehicles you do not want to tow anything while in overdrive. Its better to tow with the overdrive off. I would say for your commute you would be much better using the overdrive, as that is what it's designed for. Without it on our RPM's will be much higher and this will cause more fuel consumption. Also with mud and sand you would not really want overdrive on either, because it reduces the amount of torque to the wheels.