Light rod knock in a Durango 5.9... is it terminal?

Gas mileage sounds about right. We have an 02 Durango that we bought new. 5.9, as well. Running around town, we get 12-14 depend if I drive, or the wife drives. Ours is 2wd, so that one being 4wd, I say good luck trying to squeeze any mpgs out of it.