Totally agree. Please do check your diff ratios. As for the harsh-ish ride, please try and change your shocks before you mess with the original leaf spring setup. Just today, I changed the MMC's shocks and the difference is night and day. Having kept the RKR also, I can assure you that shocks in the rear, on a load bearing vehicle.... will be stone. So, shocks, and 1 leaf spring removed I think will do wonders. On DD's Unimog, even though it is not leaf sprung, when we added weight in the shape of soaked sand bags, the ride just got so much better that we kept smiling at each other, so I agree with your assessment during your Kalam tour.
Do you really want to hit 150kms on your truck? What's the 100 series for? And please, how many times has your jaw dropped seeing a D4D truck offroad (not rallying)? I'm pretty sure the powertrain on your Nissan is great and bullet proof, after all, that's what Nissan 4x4s are best known for. Its a carb?!? Have you seen the 4x4 Engaged Hilux? I would vote for that look and utility. Show us some photos doc!