Here's why:
* Transfer Case: The 4x4 Dakota has a transfer case, which is absent in the 2WD version. The 2WD transmission output shaft is not designed to connect to a transfer case.
* Output Shaft Differences: Even if you could somehow adapt for the transfer case, the output shaft length and possibly spline count will be different between the 2WD and 4WD transmissions.
* Computer Control: While less of a major concern than the mechanical differences, the transmission control systems likely differ between the two model years.
In short, you'd need a transmission specifically designed for a 1995 4x4 Dodge Dakota with a 3.9L V6. Trying to use the 2WD transmission would require extensive and likely impossible modifications.