Just a question about magnum swap

I'm getting about 15-18mpg around town with my stock 99 5.9/46re/8.8 3.73 swap, but that's just a guesstimate because I stop filling the tank by ear not by hose auto shutoff, AND it's at full throttle more often than not. :D
Actually better mpg than the old turbo slant and way more consistent.