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There's a lot of stuff that runs off that fuse when the brake pedal is pressed including the brake lamps, shift lock, a whole bunch of other stuff that might be shorted to ground. While you have noticed the shift interlock issue, be advised you also have no brake lights when the fuse is blown.
There isn't any easy way to troubleshoot this without certain equipment. My wife's 07 Mariner had a similar problem last spring so that it blew the brake lamp fuse when the brake pedal was pressed. I finally found a mouse nest inside the interior panel next the right rear tail lamp. The little rat had been chewing on the wiring insulation and had caused the brake lamp wire to be shorted to the ground wire, both were stripped of insulation.
I'd suggest you do a visual examination behind the tail lights and look for any other such critter carnage throughout the truck, but other than that, you'll probably need the services of a technician who is skilled at finding short circuits.