@Joe K Thank you for your reply. This is something that may also be an issue on my planned layout, curves in grades. I know what you mean about the added friction in curves.
On your layout, what type of track do you have, what are the curve diameters and Arc degrees within the 6% grades?
Also do you have any single motor diesels that work with 10 cars on the 6% grades or are they dual motor units?