Originally Posted by floydarogers
A bunch of us discussed the motor-oil change interval over on bf's diesel forum, and came to the conclusion that the usual 13K miles interval was "ok". Actually, it looks like (from Blackstone Labs reports) that you definitely wouldn't want to go much if any beyond that. 10K seemed perfectly safe. Change it at 7K if you feel you "need" to.
As far as the tranny goes, there actually is an interval: 100K miles (it's on Page 11 of the maintenance book). Personally, I'm going to do it at 60K miles.
This is how I feel also. The tranny is an expensive fix and we often don't realize how much "heavy duty" use we put it through. The 100,000 mile change interval is for "regular duty" while heavy duty requires earlier changes.