60k-80k for the first time if you get all the if you take the pto covers off and try to mop up the crap at the bottom of the case,brass,what not you may be able to go longer the next time. Really depend on how easy/hard you are on the trans.....Heavy towing,high temp can make the oil get black and coat the inside of trans,Slam shifting/agressive shifting works the syncros much harder and will put more brass in the oil. This is what I have seen with lots of 6spds