Older Dodges all have the slip near the transfer case on the rear but the fronts have it at the axle. The only thing I was told was it was to keep water from collecting in the slip yoke on the rear. The front has to be at the axle because of the Double Cardan joint at the transfer case. If it means anything, when I got my Government version '84 Ramcharger, someone had put the shaft in backward and the slip yoke was indeed worn out. After replacing it and putting it back up at the transfer case, it had no noticeable wear after 60k miles.
On the subject of phasing, another point is the angle of the yokes. All the ideas about lessening your driveshaft angles on lifted trucks with shims is wrong. The angles must stay the same on both ends of the shaft or vibration will result from the U joints elliptical pattern. One cancels out the other when they are phased correctly and the angle are the same. If they are different, one move more than the other and will cause an imbalance and vibration. The only exception is when using a Double Cardan joint. In that case, the axle pinion must be rotated up to be inline with the shaft as the two joints in the Double Cardan joint at the transfer case will cancel each other out and the third must stay inline.
Just my .03
