I bought a 2000 SD diesel and with the privacy laws I cannot find out who owned it previously. The exhaust is a 4" straight pipe and everything else took out. It has nothing that I can find in the way of a fuel control like superchips or bully dog. The turbo really spools. It actually sound like a semi when shifting through the gears. At throttle past about 2k it blows black smoke like some of these modded trucks do. Is there any at home mods that wouldn't be apparent that I could look for. I get about 16 mpg but really don't need all the extra power if it would help my mpg.