I just did the rear end diff. on my 2001 F250 V10 and followed Guzzies instructions. Worked quite well. There is always good advice on this site and I wanted to make sure credit was given. If anyone is interested, I did use the AMSOIL severe gear lube 75W 140 and I did not need to add any additional friction modifier. I have the 3.73 LS rear end.