Which transmission do you have? You didn't mention the year Explorer you got it out of, but I'm guessing it's an M50D-R1. There are a couple of different first, second, and third gear ratios that you might have, , and if it's from and Explorer, it's got the numerically lower gears.
To guys that have never heard of regearing transmissions, it's not uncommon in cars. Most transmissions on the market have different variations based on the vehicles they're used in. People have researched them to customize their gear ratios to improve performance. Usually in a car, people are trying to get closer ratios, to keep the engine in the power band most of the time.