Your not going to really get more HP out of any pump adjustment on a normally asperated diesel. Since you control RPM by fuel delivery, the governor routinely delivers ALL the fuel capacity available. Your limiting factor on HP is really air induction. Adjustments to fuel delivery only really add power when a turbo is involved to add additional air to properly burn the added fuel. If you want want more HP, you are going to have to add more air and fuel. Things like Propane injection can boost diesel HP, but like Nitrous, can come with hazards...
These tractors are adequately built for what they do. IMO if you want more HP, get a bigger tractor, unless you like to work on a tractor with limited parts suppliers available...
