OP,

If you're towing a race car with open tandem trailer, tire rack, tools and car in the 3000lb or lighter...you'll be fine with the X5.

I used our '05 X5 4.4...dealer installed hitch, wiring harness with brake controller for towing my C-Mod race car.

I had a steel 18 ft. with full steel diamond floor, tire rack to hold 4 18" rims/tires. Tools in the rear of the X5 and my race car wet was around 2500-2600 lbs.

That X5 was non sport package and towed very well. Never skipped a beat. Braking was excellent...even using stock pads. My trailer did have brakes on both axles.

The only issue I can see for you is the 3.0 engine. I'm guessing that long inclines could be problematic for you. I had to tow through mountain areas...we used to live close to the Smoky Mountains. So, having the 4.4 was necessary. There were times when I thought that the 4.8 would've been that much better.

Anyway, just thought I'd chime in. BTW, I ended up thinking it would be better getting a pick up truck...so I wouldn't trash the X5. I bought a new '05 Ford F150 FX4. That truck SUCKED. Beat you to death when it wasn't loaded and then towed worse than the X5 when loaded. Needless to say, it got sold!
I was going to upgrade my trailer for something that provided living quarters and car hauler...so, I bought an '08 Dodge Dually Mega Cab with the Cummins. When the economy tanked...I was left holding the Dually as a daily driver and didn't get the larger trailer. Hated driving the dually...Oh the mistakes I've made with tow vehicles!!!

If you're only towing to 5-6 events per year...I wouldn't spend money on another vehicle that you'll hate driving for anything but towing.
If you're new into the racing scene...go with what you've got and see what others are doing and their experience.
I found that a lot of guys were using their X5's for towing OPEN trailers...but I've only seen V8's doing the work...not 6 cylinders.

Good luck. The X5 in my experience was very capable for my towing needs.

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2002 4.4 Sport
134k miles and counting