When I researched this for my truck I ended up going with the Chromo Axle Shafts from Poly Performance and did not go with teh Chromo Birfs. Reason being ... everyone I spoke with said the Chromo Birfs wear much faster than OEM. They are tougher for sure ... and needed if you are running way oversize tires ... but they do not wear like the OEM Birfs.
FYI - This is based on a lot of reeacrh ... not my own experience.
altanta custom creations is having a sale on chromoly longfields, 750.00 for inner, and 30 spline outters. shipped to your house. talk to mike, i delt with him, he is a really good guy, and really helpful. i ordered a set, and they are great.