OK so I feel I am stressing the truck to much in hilly conditions pulling my 5th wheel camper, seems fine out on open road but needs help near the lakes and camp grounds going up those sometimes large...
Find an online gear calculator and work out some final ratios/speeds/rpm. I went from a 97 CTD 3.54 to this 03 4.10. The 97 had way more power mods and would blow away the 03, empty, but the 03 pulled the hills just as good, towing. Lower diff gears also put the trans gear rpm splits closer together and make the vehicle do everything easier. 4.56 sounds like too drastic of a jump to me but I don't know exactly how you use the truck. Craig