ujs, pinion bearings, output shaft worn, drive flanges worn, diff bearings allowing play between pinion and crown wheel its a long and exhaustive list that is barely covered here. dont be silly and work it out yourself there is a lot of wear and tear on a 2.5 tonne landy dragging its arse about. you say you have a tweaked pump so you probably wanted it to be quicker- well that will wear stuff out faster too.
honestly its been covered a thousand times and it is usually a combination of most of the above. just start twisting banging and abusing stuff til you find the main culprits then change em and move on to the next part, when thats done move on to the next when that is done the next and then back to the first and start again. its cyclical and if you find a one stop answer that removes the steps above then let me know would you because it would make my life a lot easier.