e70 are cool but also suffer from the valve seals if you're looking at the V8. And while the 4.4 and 4.8 may share the same type of engine they don't share the same power and the trim is different. IMO if you can get a 4.8is that has been well maintained and already has the valve seals done and some of the other issues taken care of, the truck will run well into high mileage. It's all on how the truck has been maintained. I love my 4.8is and over the past 2 months I've spent about 3k doing the seals, air suspension, control arms and regular maintenance and she runs beautifully, and I plan to keep her for a long time. Mine only has 106k and I drive her maybe 2x a month.

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2004 BMW X5 4.8is