The setscrew(AKA grib screw) known as 86094 is the culprit 9 times out of 10. Check the rear of the tranny where the brake disc is, look into the center rear dog bone cup that mounts to the rear output shaft, and check to see if that stupid setscrew, 86094, is still there. If not, but a bag of replacement 86094's and replace, very simple.

If its is not 86094, check the other setscrew on the other end of the cebter rear dogbone that goes to the rear diff. This setscrew is called 86095. If that is still there, you will have to remove your rear diff and inspect the bevel gears.

To quickly rule out stripped diff bevel gears, roll your Savage on the ground forward and backward by hand. If a really loud "click!click!click!" issues forth, the 13T/43T diff outer bevel gears are stripped and/or the spider gears inside the diff cup are stripped.