The Super Duty name was used on trucks starting in 1999. These trucks are different from their non-Super Duty counterparts because they bigger engines and frames made to take a beating.
Engines available for these trucks include a 5.4 L V8, a 6.8 L V8, a 6.8 L V10, a 7.3 L Powerstroke V8 turbo diesel, and a 6.0 L Powerstroke V8 with variable vane turbo.
Transmissions have included a 5 and 6 speed manual and an optional 4 speed automatic.
Aside from greater carrying capacity, these trucks also tend to have a lot more interior room and much more towing capacity. They are based on a completely different platform than the F-150, although they are still considered to be a part of the F-Series.
These huge trucks served as the base platform for the Ford Excursion, a short-lived monster of an SUV that was derided for its excessiveness.
These trucks are very popular with businesses that need heavy duty equipment. They can be equipped with towing equipment, among other things. In fact, it's almost pointless to be driving one of these trucks except for commercial applications. You can find them being sold used, although they tend to very popular with owners. Expect to pay a high price for these trucks, even used. You can save some money by buying off eBay.