few questions - 1) i recently got 3.90's installed and im currently breaking them in... the place that installed them said i should get new gear oil? after the 500 mile break in... what does he mean exactly? differential oil replaced? tranny fluid replaced? 2) who can do it, how much does it usually cost, and what kind of oil should i replace it with? 3) My car is sort of new so i still have warranty plus the maintenance package- will Ford replace my fluids when i go in there for regular oil changes n such? and if so will that have an impact on my gears?ie. due to different type of oil(ford stuff) thanx in advance