Pardon me if I'm telling you what you already know, but it's not the PTO like on a tractor. On a truck it is an access plate on the side of the transmission (or transfer case) that allows you to install a geared assembly (pto unit) that gives you a small rotating shaft to use for aux items. These are usually a hyd. pump that can be used for operating a dump cyl, snow plows, sand/salt spreaders, etc.
In years past they also powered mechanical winches (tow trucks). They have been available for years on most all "vocational" trucks, and kinda faded in PU's as they (PU's) became "yuppiefied" with more buyers picking up the groceries, than a pile of lumber. High fuel prices and the new 15,000 - 18,000 gvw duty trucks are filling in the gap between 1 tons and Med. duty trucks, and have been very popular with contractors by staying under the CDL 26,000. All of these trucks are delivered to the dealer as what is called a chassis/cab, and will end up at an "upfitter" (truck body shop) and have the unit comleted for end customer. A service (tool) body truck might have a generator or an air compressor driven off the pto. I have a 99 F450 with a PTO off the trans. running an intergral hyd. pump for the dump hoist. I even have a '01 F350 single weel PU that I ordered with the PTO access onthe trans. I never used it but it was only a $60 option, so you can see, it;s not new, but maybe gaining in popularity, that;s a good thing. Way back you could get 3pt. hitch and a reg. 6 spline pto at the hitch from the factory on a CJ Jeep!!:thumbsup: