hi all now i have the series 2a up and running and using it a lot more i have been thinking of changing the diffs .due to it reving its tits of at 45 50 mph its a 2.25 diesle .i know this can be done but what diffs should i be looking for just to bring the revs down and give a bit more road speed and what price should i expect to pay for the diffs any info on this will be helpfull thanks .before i buy the wrong stuff off ebay thanks