Dark greens are exactly that buddy so although I cant tell you what they are for sure they sound like standard 4x4 if im not mistaken, the -31 is a dash 31 and has probably been put on at some stage in place of a knackered standard one and not always part of a stage 3 conversion.

With regards to the ECU you will have to pull it out and check out the numbers but its doubtfull given the info you have supplied its any more than a standard L6 but even that can be chipped for good power, if its a standard chip and ECU I would say about 15psi max before it chops back and even less on a cold day.

All of this im saying from experience so dont slaughter me if im not 100% but im sure the other guys on here will know for sure.

Jase