2 speed rearend help. gear ratio

I have an 89 international single axle,2spd rear end with 5.57 ratio(tag), 5yrd gallion bed.

a 7.3 diesel, 5 spd trans, and when I am taching 2500 rpm I am only running 50mph.



I need to get about 65mph at 2200, save my engine.

I have to make 50 mile round trips and the guys are gonna run me over since I cant run any faster when I need.



can anybody point me to correct direction? I found a source for complete used rear pumpkins($500), but I need to know the correct gear ratio.



any help would be appreciated.

2 speed rearend help. gear ratio