My 2000 ls470 seems to be losing power when climbing steep grades. It has about 125,000. I realize it is a heavy vehicle, but I get the idea that if I was pulling a trailer it might not make the grade. Any ideas what may be going on?

 

Check brakes, if your parking brake handle is loose check for stuck parking brake eng mechanisms at the end of the cable on both rear wheels, remove the spare and get under the rear of the car.

Also rusty brakes can be stock on either wheel.