Thanks so much for the prompt feedback & advice. Love this forum...
I'm going to try different diff settings for the both front & rear. Just added the belt tensioner after seeing the belt moving upwards at full revs on my 9T BL. Cannot imagine it sawing one of the wires....
Just wondering would fitting a fixed diff for the front be a better choice than changing oil type? Would Maintenance be lesser and easier for my son to learn driving it? The cost of the part is roughly the same as a branded diff oil.