Turbo going out 2005 - replace cartridge or upgrade?

Father in law's turbo seals are going out. He has an 05' and he said he would be willing to step up the turbo size. He tows his backhoe once in awhile. Truck is stock other than a banks six gun. Would just replacing the cartridge be the best bet ? I've rebuilt a few holsets.
T I A

What about this or an equivalent from a site sponsor ?

http://usdieselparts.com/i-13464737-garrett-powermax-stage-1-turbo-04-10-gm-duramax-lly-lbz-lmm.html