It seems from your setup that you have an 8 tooth drive gear. A 23 tooth speedo gear would get you the closest, but the calculator says you need a 25 or 26 (which the don't make). You would need to change out your drive gear
Taken from the 5.0 Tech: Technical index: speedo gear part #'s and information Manual Transmissions with 8 Tooth Drive Gear
1990-1995 T-5 OEM
1996-1998 T-45 OEM Except Cobra
Item Number
Description
Jeep Part #j3167393
4.10 Gear Ratio / White 23 Speedo Gear (Not 100% accurate. This combination will offer the best accuracy without changing the drive gear. Change drive gear to a 6 tooth for complete accuracy. See 6 tooth table.)
Yep its the same one as 3.73 gears. Its not accurate with the 3.73 gears aswell. If your into it the t-5 needs to come apart to swap the drive gear out. I'm in the same boat. One day.
Yep. A 15% error is exactly what you'd expect with the 8-tooth drive gear, and the 23-tooth driven gear.
If you replace the 8-tooth drive gear with a 7-tooth gear (yellow), the 23-tooth driven gear will get your speedo reading about 3% slow, which is pretty good.
But as long as you'd be changing out the drive gear, you could look for the 6-tooth (black) drive gear. With the black gear you could use a 19-tooth (pink) driven gear. That would get your speedo almost dead on (according to the theoretical calculations), and the 19-tooth gear would not get chewed up like most 23-tooth gears do.