Ok I have a 85 cj7 settin on 38 tsl with a 304( it came with online 6) t5 dana 30 in front and amc 20 in rear pretty sure its 2:73 gear ratio as I can't get past 3 rd gear I am wanting to put lower gears in it I know I have to change carrier in front to put 4:56 do I have to change the rear...