diff/trans/t-case service

[salyers890]

I'm about to hit 20k and never seen any serious rocky or muddy play. I've towed a heavy boat about 10 miles, and been on a 400+ mile road trip. I'm thinking now about changnig the fluids in the diff/t-case. At what intervals do you guys switch out the lube? how about the trans? do you wait and do the flush, or do you change the pan/filter incrementally every xxxx miles on the auto?

[moneypit]

I have changed the diffs, because I put on Rockcrushers. Have not done the trans or transfer case. I have 25K on it now. Maybe next spring I will do the others. Most of my cars I don't do the trans till 75K or so.