We're considering a newer X3 for daily use, which would free up our 2004 (E53) X5 4.4i as a weekend tow vehicle (replacing a string of Jeep SUVs from 4.0L, 5.2L and 5.9L, mainly for the beefier trans more than displacement, as the race trailers gained weight over the years). Duties will include hauling a 10K gross trailer with WD hitch at speed for up to half days non-stop at a time, from about -10F to +112F. I've already grabbed the heavier pre-facelift OEM hitch, although the facelift version's holding so far. For drivetrain lubes, I'm either already using or moving to:


N62 4.4L engine: 10W-30 full synthetic


Rear diff: 75-140 full synthetic


Front diff: 75-90 full synthetic


ZF Auto 6-spd: ATF+4 full synthetic (since BMW/Lifeguard6 is apparently just Mercon SP dino oil)


X-Drive transfer case: Need further advice (understood NOT ATF, but is the stock BMW fluid full synthetic or is there anything better?)


I don't want to make this a brand discussion, but any comments on proposed fluid specs greatly appreciated! It has the factory trans fluid cooler. Is that likely sufficient, or should I go bigger? Any other coolers needed for summer towing? Thanks in advance!