calibration kit

Which jets in a calibration kit would I use to get better gas milage

If you're talking about jets for your new Weber, then smaller idle jets may help gas mileage. But don't screw up your idle or running chasing some holy grail claim of 28 mpg, these trucks don't do that.

My mileage before and after my Weber 32/36 DGEV kit were the same, like 19 mpg (Cab Plus, AC run most of the year). I did my Weber in late 2005 because I was having running issues, and my mechanic thought it was carburetion/ECU - but he may have been mistaken, as my distributor components turned out to be iffy at the same time.

To make sure you are using the right jets you should be looking at your spark plug ceramics. You can jet a carb so lean that it leads to detonation. Proper color for plug ceramic is a caramel brown. Best mileage I ever got with my truck and stock carb was 24 mpg.