There are vector units and turbo booster for it (3.2) to come close_to/beat Navara's power... You may get the 2.5 to the 3.2's default power... to get the 2.5 Triton to Navara's would be difficult/damaging to the engine/gear system. Any of these sort of mod voids the warranty...

Tritons are know to suffer gearing problems/failing/inferior... and Frontier/Navara (s) have engine blowing up incidences in UK...

The Hilux and D-max are tough and durable (and frugal for D-Max)... but are not powerful

go for hilux...or ranger...

At default... 3.2L's the torque still lack behind the 2.5 Navara, by a huge margine, Mother Trucker, one for the top Dog in 2.5L Diesel engine .... Give and take... each has its own points...  Road tax does not really matter for Sabahans..

powerful?..for what...

hilux

nah, i've tested all sometimes ago. the navara does feel more powerful than the 3.2 triton but, in triton,
the engine linear is smoother compared to the navara. perhaps, the 'urge' in navara will suit your
taste for powerful diesel car 
i see no point in buying a 2.5 triton and jack it up. it won't be able to get near the navara in term of power.
spending extra on engine reworks + bigger turbine will only increased the cost and possibly void the warranty.
btw, there are s limitation on 4 cylinder turbo engine. no matter how you crank up / modded it, you will eventually reach a limit where the engine can't take the 'punishment' anymore. and the internal part might just give away 

since i used to travel frequently to sabah, imo, driving a manual car is more fun.
the hilly terrain/road punish the auto gear box more, so, the service interval for auto gearbox is a lot more earlier
than the manufacturer recommended interval. perhaps, installing an ATF cooler will help.
if you can wait, there is only one truck that matter most and it was the navara 6 speed manual which is currently
only available in Thailand but i doubt ETC will bring 'em anytime soon.. 
the monster hilux in UK will not be able to breath in our current diesel quality.

go for a test drive and feel for yourself. nothing beat the feeling of getting a hands on experience.