The GM 390r transmission was for the six cylinder, in all markets. The ZF 6hp transmission was for the V8 models, in all markets. The diesels changed from early models to later models due to torque capacity of the GM transmission.

Trailer stability control is in the DSC, not the trailer package. I even have it on my E83, which is an E46 platform. It is activated by the factory wiring harness being connected, but it is already there, just dormant. Coding isn't required, as long as your vehicle software recognizes the towing harness.

You don't need a Cummins, that's an engine. You may need a 3/4 ton pickup.

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2007 X3 3.0si, 6 MT, Premium, White

Retired:
2008 535i, 6 MT, M Sport, Premium, Space Grey
2003 X5 3.0 Steptronic, Premium, Titanium Silver
2002 325xi 5 MT, Steel Grey
2004 Z4 3.0 Premium, Sport, SMG, Maldives Blue