I have a 2000 SD, 7.3 with a bad rear end. My sterling axle code is 406H with an open diff. The best I can find on the net is 100-200 serial number axles are for gassers and the 400 series are for diesels. Of course, all the local junk yard axles are $100 to $300 for the 100 to early 400 series. Then my 406H is $500. I struggle to believe there are 30 differences in all the series and why would the 406H appear to be an outcast? Any information would be great. Thank You Very Much!!