Did you put larger tires on it or regear? If so, the
Truspeed Calibrator will fix it for both of those mods. Install is super easy, but takes a little time with removing the gauge cluster and soldering the calibrator into the speed sensor wire. It's listed as being available for the 1992 - 2005 Tacoma, so it should be fine to install it.
Check out
this thread on how the install went on a few 1st Gen Tundras. The principals are the same, but your wiring is going to be a bit different. Before you rip into it, shoot
mustang67408 a PM or email with your truck specs (year, make, model) and he can probably give you the exact speed sensor wire you need to tap into.