Definetly not normal. They should both be 4.56, or at least within .01 of each other. According to my 4x4 guide, neither ratio was available for a GMC that year in a 3/4 ton. It sounds like the axle have been changed. Question-Is the front open or closed knuckle? If it's open, then it's a '69 or later axle. You definetly need to get both diffs with the same ratio. T-case damage can result with the difference that you currently have.
