Trim the pork of all fat and silverskin.
Generously salt and pepper the tenderloins.
Melt 3 tablespoons of the jelly in a small pan over low heat and brush over each tenderloin.
Rotate the pork, one on each spit rod, 30 minutes or until the internal temperature reaches 150 to 155 degrees on the instant thermometer.
While pork is rotating, heat remaining jelly in a small saucepan and stir in the sour cream.
Warm slightly, but do not allow to bubble or it will curdle.
Slice tenderloins on the diagonal into 1/2-inch medallions, and serve with warm sauce.