[gmc 2500 4x4]

im having a slight issue, 69 gmc k2500, all redone, i went from 4:56 gears to 3:54. it now has a bb 402 and original sm465 trans, and rockwell 221. im getting a shudder when slowing down in 2wd, even when i push in the clutch. would the gearing change affect the t/case? has a 4'' lift also, and i did shim the rear axle for driveshaft alignment...