cdawall

after throwing 33s under my XJ i have noticed i lost some MPG's and alot of torque freeway driving up hills. there is an older XJ with 200kish in the JY with the 4 banger 4wd and a stick from what i understand it will have 4.10s in it. should i snag the axles out from under it and throw them in my jeep? i have a D30/35 and so does it. however its an 80s with a the CAD and D35 non-cclip from what i was i reading i can take the CAD and stuff my current shafts in it since for one they are the bigger ujoints and for 2 they are non-cad. would it be a worth upgrade? should i just try and grab the gears/carriers or what...i have never done a gear swap before and shop quotes $360 for front and rear.