they did make duallys but only in 2 wheel drive the 4wheel drive ones were dealer or customer done. they were pretty awsome trucks and im pretty they did stop makeing them in 93. the only problem was they were mostly automatics, but they came with like 4.30 gears and heavy duty transmissions. they also made 1 ton, 2 and 4 wheel drive pickups in the early 80's.
I bought a 1991 1-ton dually cab and chassis new from the dealer in 1991, then had an aluminum bed installed by a truck body shop. It was an awesome truck for my construction business at the time. The ones that were typically sold through dealers had the same drive train as the RV's. I too always thought a 4x4 version would be nice to have.