why would the T-5 be too light duty for a 148 HP engine? The 4.3 puts out a whopping 180!
Try gettinng the truck loaded up with dirt or gravel, and then hit a section of washboard road on a hard pull- - - - -the inertia of several times the weight of the vehicle the T-5 was intended to work with will take teeth off the gears like shellng an ear of dried corn. The gears in the SM-420 weren't over-engineered for no reason at all.
Jerry