If it were a K1500 or K2500 I would say no. But you're dealing with a K3500, so that's a whole nother level. I know the higher level commercial trucks have it as a factory option, but I'm not sure about the K3500.
PTO stands for Power Take Off. It allows you to run devices off of the engine, but through the transmission. Popular items to run off of PTOs are pumps, generators, and sometimes other mechanical devices (can't think of any good examples). On lawnmowers/tractors, the shaft coming out the back that usually connects to a grass cutting deck is a PTO. To answer your question, I would think that you would have to get one of those commercial grade trannies to even think of getting the PTO option. I don't think that's something that could be built into a regular run-of-the-mill tranny....sorry for the bad news.
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