I'm having an issue with the #2 fuse blowing on the interior fuse panel, the one that controls the O/D, Blower motor, reverse lights etc. I already rewired the blower motor resistor connector with a new one trying to weed it out. It only blows when put into drive if that helps finding a solution.
Check grounds, and check the components powered by that fuse for excessive current draw. A 21-year-old blower motor would be a prime suspect.
You could go under the truck and unplug the transmission range sensor.
Then try shifting from Park to Drive. If the fuse doesn't blow you've narrowed it down to either the transmission range sensor or the wiring to the backup lights or the backup lights or light sockets themselves.