The original t-box was a 1.4 & the disco one i fitted is 1.222, this is on my td5 90 with EGR removed, non cat front pipe & centre box removed, I am seriously impressed with it, will pull past 100mph on my private test runway with more to go.
Cruising at 70mph is now only 2200rpm in 5th gear this is all done with my 235/65/16 summer road tyres, I guess when i fit the special traks I will lose acceleration & gain even more top end, the truck has loads of power so i don't think it will be an issue, if it is I have a dastek unichip buried in my toolbox somewhere, so ill chuck that on for the extra pulling power !!
Transfer box cost me £50, I replaced the seals & chucked it in, very worthwhile mod i reckon !
I do have a used GKN if anybody wants to make an offer on it, came of a working truck, not sure on its condition though, i certainly won't be fitting it, think the wheels would fall off if i went any faster!