Sheleen
Firstly - Welcome here!
Calling any suspension change an upgrade is a bit of a misnomer as it actually is a change of the current setup to accomodate a change in use/requirement. With this change you will upgrade certain areas(load carrying ability, ground clearance possibly) but you will also downgrade on other aspects with that same change(stiffer less comfortable ride, higher center of grafity, possibly more body roll). So please be aware that there are no suspension system in the world that can do all things for all applications, but rather a trade off to get closer to ones own requirements, no matter what any salesman out there tell otherwise
OK, so after that bit of useless info, here are my recomendations.
Firstly do a search on this forum as there are many examples and previous discussions on this matter in the past that might already answer your questions
Secondly, given the speech above, there are no perfect system out there although some might be better suited to a specific persons requirements. None of the aftermarket dampers/shock absorber on the GEN3(2000-2007) Pajero is of a longer length than the standard one so none will give better articulation or increased travel, no matter what the sales people tell you. You will gain some ride height increase due to the longer coils fitted by most suppliers and if used on most off road trails this could be a nice addition.
I like the following suspension systems in order of preference:
- Old Man Emu
TJM Extreme
Iron Man(not my personal choice)
I would also look at just changing coils with coils from Van Zyls springs and put in Gabriel HDP(Good value for money) or Monroe shocks
Definately look at increasing load carrying capacity at the rear with Air Suspension addition which has the nice feature to work when needed but otherwise drive like normal.
CATS