Are the diffs different??

I have a 90 with a 200TDI disco transplant and a 1990 RRC rear axle.

Is the diff in the RRC axle different to what should be on the 90? If so how would this affect gearing?

Engine now runs spot on but LR seems a bit slow on accelaration and top end for a TDI. Could this diff affect this??

Thanks.

as far as i know the gearing in them is the same. What transfer box is on it?