Ratios are as follows unless you have the v8 spec 5th gear, yes you need a different tail shaft:

TREMEC tko600
1st 2.87
2nd 1.89
3rd 1.28
4th 1.00
5th. 0.83

T5
1st = 2.95:1
2nd = 1.94:1
3rd = 1.34:1
4th = 1:1
5th = 0.80:1