http://store.realdiesel.com/gmch6inpu.html http://www.o-f-i.com/index.php?pid=1...INJECTON_PUMPS
Check out these links, there are many, many, links that end up on e-bay. With a little shopping I think you could do better.
Make sure you get the instalation kit, as this will have some wear parts for the pump drive. The second link has new pumps for your instalation, the rebuilt units are further down the page. Also, it looks like they have some pumps for "heavy duty" applications, this might give your truck a little more get go.