Telma Frictionless Retarder
Saw a pic of one of these units over at TDS. The rig it was on was an F-550 set up to transport RV's cross country. It was mounted in such a way that it replaced the carrier bearing. Basically the idea is that you introduce an electrical field to a driveshaft-mounted rotor and the result is a retarding force on the driveshaft. From what I have read it can be engaged in four stages depending on the braking force needed.
I'm not sure what kind of electrical loads would be created, but I think it would be safe to assume that you would need a healthy alternator to keep up with it.
Those things work fabulously, and are fabulously expensive too
I've never seen one on a pickup, but if you are ever up in some of the real hairy areas of the pacific northwest, like around Lewiston Idaho, don't try to follow one of the chip trucks pulling rocky mountain doubles off a mountain because you WILL loose your brakes halfway down... while the guy in front of you hasn't touched the pedal the whole way ( don't ask how I know this
I don't know what the current specs are, but 25 years ago they used to brag that you could go down an 8 % grade with 80k pounds and not have to touch the brakes. Most of the heavy haulers in that area were putting the things on the trailer axles. Around there I imagine the units paid for themselves in reduced brake maintnence in about 9 months
At the time I really wanted to get one for my rig, but couldn't afford the thing