g'day Spud
a few years ago i worked for a diesel chip supplier /fitter
at that time they were doing a lot of R & D on the amarok
(sorry but know nothing of the unit you're asking about)
stage 1) fitted a rapid chip and exhaust
stage 2) rapid out tunit in
stage 3) tunit out and flash tune the ecu, this option gave the best upgrade and reliability
over a few months they tried quit a few different tunes until they found a tune that was good on fuel with nice power upgrade
now i have not been with that company for 2 years, but have heard that they now do their own ecu tuning and stepped up the R & D on all makes of cars and 4wds.
after seeing what they can do and the difference between chips and tunes IMO the flash tune looks to be the better option
also one of the best power upgrades i noted in my time there was the INTERCOOLER on some 4wd's this made more power than the chip did
and IMO there is no need for a 3" exhaust on a 4cyl diesel, instead save your $$$ and replace the muff box with a high flow unit
Adam