Thread should be in 5T mod section.
I'd either buy a tired Cummins 400 turbo (can be had cheap) and rebuild it, or swap in the later 8.3L turbo and turn that up. With the 8.3L, you will double your fuel efficiency also. In addition, the lighter 8.3L engine will help it accelerate quicker also. If you have a little bit more $, you could swap in a used Detroit Diesel Series 60 or Cummins ISX, both can be had in +500hp versions. If you want faster top speed with the same drivetrain you have now, the 8.3L with performance governor springs and the fuel rack turned up would be nearly the only way to do it, as it is one of the only candidates that can spin higher RPM without putting holes in the block. Goes up to 3400rpm in marine apps.
Besides the duel fuel line and fuel button as mentioned above, your options are kind of slim. A few here have put turbos on them, study those threads, figure cost vs reward, go from there.