At the risk of sounding biased, Go with the ford. The engine in the GMC in my opionon will give you better milage and more power. Probably also engine work will be cheaper on the GMC. A 302 isnt underpowered in a 3/4 ton, regardless of what the chevy guys will tell you. Granted the chev 350 is better, but test drive the ford and see for yourself. But:
1. lifting the GMC is gonna be expensive, Ford suspensions are much cheaper to work on. In '88 chevy went from a solid axle suspension to ifs. If you really must buy a chevy i would ger one at least a year older so you can get the solid axle. Either truck can be great off road, but the ford is going to be cheaper to modify, and its already a 3/4 ton so it will be stronger.
2. Stepside beds are abosolutley completely useless on a pickup. Why would you want a pickup that cant haul anything?
3. No comparison on strength and durability, if you want an example, look at service vehicles in construction and logging for those years and see how many chevy/gmcs are in use compared to fords. The fords far outnumber anything else (fleet service vehicles) here in oregon, and i would assume its the same all over. Not trying to knock the GMC, i would drive one if i had one, but given a choice of 1/2 ton chev or 3/4 ton ford, ill take the ford. The only advantage the GMC has is the engine, but ford makes a better overall truck. In my opinion toyota makes the best pickup on the road, but if you need a fullsize pickup, there is no comparison, buy a FORD!
93 F250 7.3 Diesel, 4 inch tuff country lift, 35 inch Wild Country's