First of all, I don't think any first gen ever came with a 3 ton towing capacity, although I have towed more than that. Second, Its not that a lift itself is harder on the truck, its often the bigger tires that come with it. In general, most of the lift kits available are geared to off road performance. In my experience, this hurts towing performance. You will have to give more info on what exactly you are trying to get out of the truck, but I can tell you that you need a minimum of a class III hitch to tow 6000 pounds. Re gearing can compensate for bigger tires, and depends on what size tire you choose. A lot of guys go with 4.10:1 because you can find them in stock axles if you look. One worthwhile upgrade if you do go that route is to find a rear axle with disk brakes. The 4.0 OHV makes more than enough power for towing and off road. The weak point will be the auto transmission, assuming you have one. Keeping it cool is the key. An aftermarket tranny cooler (with external filter) is worth its weight in gold if you plan to tow a lot. That said, I never ran a cooler on mine and it still works fine 220k later. Out in the country, I was always conscious enough to get up to speed and let the torque converter lock. If I lived in the city, or just did lots of stop and go, the tranny would overheat in no time. Long story short, the brakes and tranny will be the weak points. You will never ruin the rear axle, however, running too high of gearing will be harder on the transmission. If you have the manual M5OD, you have nothing to worry about.
