Geoff,
The short answer is "it's always better to keep what you have and make do with added appurtenances." (a Quebec-ian term)
2003 was a good year for the CTD, if underpowered compared to the present offerings. If you have a quad cab you can make do with what you have with 2 small ninos. AFA taking more stuff along, why not consider a small enclosed trailer for the kiddie goods? What i did not like was the big space that would appear when putting, i'm assuming, a short bed TC on a long bed truck. The center of gravity would be not good. 3750 load rated tires are plenty good enough for your purposes. If you want a wider rr footprint you could, like I did, go with 12" wide wheels and 14.50 wide super singles. I added some Jeep TJ, 7" fender lips on the rear axle.
My vote would be to keep what you have and make it work.
jefe