When I replaced my starter in 2008 with a lifetime guarantee from NAPA, the part number was 46-4078 which is now an obsolete part number. Running the part number through NAPA's Interchange application, I come up with four different options at NAPA priced from $85-$124 depending on whether they are re-manufactured or new. See these at
http://tinyurl.com/d73ssx8.
The Correct AutoZone part number is DL4346S. They have it for $59.99 re-manufacturer with plus a $10 core charge. And yes, the starter for our GMC V6 engines is the same as one for some later model Chevrolet motors. Hope this helps.