You are looking at an 05. I had an 06 with the HD tow package. Tow package is 6900, without it is more like 5900.
the truck was well suited for 3500-4000 pounds. That was comfortable and would pull 4000 for hours quite nicely. Note I did have new shocks all around. 5000 became a little work. 6000, I did a lot with it (all interstate) and that was ok to 55mph and absolutely no fun above that.
if it doesn’t have the quad piston calipers, walk away. The brakes are limited but the quad calipers will work nicely for 4500 lbs, but a real problem at 6k where we were.
the 06 has a better transmission for towing. the 05 has a 4 speed, and OD is known for being over-stressed if you try to tow in 4th (don’t).
My 4.7 was a phenomenally well-built motor. Mine had 150k on it when we sold it. All 3 owners towed with it, and the engine/transmission ran and shifted like a new car, used no oil, was dry as a bone outside of a minor valve gasket weep. One of the most reliable vehicles I’ve ever owned.
only other caveat is this - towing without OD introduces a little rpm’s up front. My oem exhaust sang a sweet song… and could get loud at 5 hours of 2700 rpm. Looking under the shields, they were not manifolds, they were basically tri-y headers. Wow. It’s commendable that they would do this in a factory vehicle, but tri-y’s aren’t quiet when you’re working the truck.
also, towing 6000 lbs through the mountains in gruelling summer heat with the AC on? Air stayed cold and the engine never overheated. I had a temp gauge on the trans and it also stayed cool (it stayed cooler out of OD). You’d know it when the fan clutch kicked in and it would sound like a small dump truck - quite impressive vehicle, and perfect size in town.