Common problems on the 4x4's are the plenum gasket blowing which would cause pinging & poor performance. The tracbar goes out too soon... some as early as 40k miles. the tranny's pretty much suck.
for all of these there are some good fixes...
http://www.apsprecision.com/ for the plenum fix and a bullet proof tranny
http://www.solidsteel.ca/news.htm for the tracbar fix. it uses a 2003 tracbar that doesn't have the ball joint on the end so it'll hold up alot better.
As far as towing goes... get the biggest tranny cooler you can get on there and it will help alot. For power upgrades, there are tons of things you can do if you choose to, but keep in mind the towing side of things... you'll want mods that will not loose low end torque. If you get to the TB upgrade, still get the 52mm TB, it's worth every penny.
hope this helps