2000+ mile road trip in the Duster, going to be heading up I-84 on Monday

The best I have got, has been 15.8 mpg and the worst is 12.2. The car is set up for about 200 feet above sea level and the first legs of the trip were the best milage. Now it's a pig and getting more around the 12 mpg. This is the first time I have ever ran a holley, and I did rebuild it myself right before the trip. First carb I have ever rebuilt too. The kick down is also not working properly. It won't kickdown unless I have it set really tight, but then won't shift out of second till like 50mph. I am using the Loker set up. Don't really know what to do about that.