Has anyone used the amsoil 75/140 severe gear oil I have a 29 outlaw pushing 640 each was just wondering if this would be a good choice

Yes, I have run both 75-140 and the 75-140 with a little 190 in it as well. I think I did 2 of the 140 and 1 of the 190. But IMHO what you gain in gear life you lose in the cone clutch. The bravo shop doesn't like Amsoil for this same reason.

Look up Mystik 85-140. I switched to it and I like it. Its badazz stuff especially for the price. I think it has as good or better shock loading qualities than just about anything I have used.

I have a stage 4 merc 600 with 200 hr using amsoil in stock xr drive.

I have used Amsoil 75-140 for years in my Bravo1's with no problems at all,,

I've never had an issue with Amsoil either.

I use it as well