Diesel Bombers - Hello from Santa Cruz

Hey guys,
I have a 1992 w250
I have a compound turbo setup installed professionally from the previous owner, this truck is seriously underpowered for how much it has strapped to it.
I have been reading LOADS and am reading more about tuning and head studs ect.

The Stock turbo is compounded with one off a Kentworth diesel-
the PREVIOUS owner says the pump is "maxed out" and there are upgraded injectors but didn't know anything else, so I am reading EVERYTHING I can to use this potential.

The truck has 350k miles on it with 120k on the engine.
I just got a new trans from a member on here and am in the middle of installing it. When I pulled the old tranny there was a blue torque converter- Obviously aftermarket of some sort but I don't know.

ANYWAY! Thanks for the awesome forum I have been given the opportunity to be a part of. Hopefully I can some day be a source of knowledge and no longer the one asking idiotic questions.