I calculate that the 2016 Colorado 2wd diesel will climb an 18% grade at 55 mph steady speed at max power, towing a 2,000 lb trailer.
I assumed 160 hp actually reached the ground, so I'm assuming about 21 hp was "lost" due to wind drag, drivetrain losses, tire losses altogether. Maybe I was being too generous with that 160 hp reaching the ground.
P watts / (W newtons * speed m/s) = grade fraction (small angle approx used)
P watts = 119,00 watts is 160 hp
speed m/s = 24.6 m/s is 55 miles/hour
W newtons = 27,000 newtons is 6,000 lbs
grade fraction is 0.18 result
If you assume only 140 hp reaches the ground after losses, then
the result is a 15% grade.