I tow 4600 lbs with a gasser. I get slowed down to about 80 mph up a 6% grade. I'm running somewhere between 420 and 440 HP.
In you original post you stated both engines you were looking at were 300 HP. Assuming optimum gearing, both engines are going to pull your 6% grade at the same speed, regardless of their torque rating. HP always tells you how fast you will go up a grade. Torque will tell you how often it will downshift on smaller grades. When comparing your gasser to those DPs, assuming limited altitude, those 300 hp DPs are going to be slower than your gasser on steep grades. The only advantage is the DP does not loose power at higher altitudes. If you want more power, then you have to buy more power. I'm betting 450 hp or more is much more likely to satisfy.
