Fuel economy question?? 4th unlocked vs. 3rd locked

[D. Showan]

190 degrees isn't that bad if it would stay there and not go any higher. I figure my GCVW is only about 14,500 so with the addition of a 250 hp. fuel plate (hopefully soon) I should be able to stay in 4th locked most of the time on hills(I'm usually going 65+ on the flats). If I can't quite make it to the top without lugging, I should be able to unlock for a while at least and maybe get over the hill if it's not too steep or too long