What year is your truck, I can move this thread into the proper location.
Here are some simple instructions.
What gear ratio do I have?
Jack up one tire if you have an open diff, or both tires if you have a working posi or locking differential. Rotate the tire one full revolution for posis and lockers and 2 full revolutions for open diffs. Carefully count the number of full revolutions the driveshaft makes. This is your gear ratio. In other words, if the drive shaft turns 3 ¾ turns, you probably have a 3.73 gear ratio. Turning the tire for twice the number of full revolutions and dividing the drive shaft revolutions by two will give you a more accurate reading.
I dont know if its all the dakotas but i know for sure my 5.9 rt is built and geared for low end torque, off the line its a beast, long run though not so much. Its more of a 1/8 th mile truck rather than a 1/4 mile.