guys, gotta 02 tacoma that calls for 75w90 gear oil for the diffys.. i want to go up to 75/140 not 75w110 (bc my local amsoil guy doesnt sell it and i wont pay for a case at one time) but the 75w140 is M1 or other synthetic gear lube. my question is i dont pull much just a bass boat once in a while and my driving is 80% highway.. going up to the 140wt, could i extend the oci to 50k miles? instead of book calling for 30k miles?? my amsoil dealer does have 75w90 severe gear which i am really thinking about and running it to 50k miles and change.. what do you guys think?