I was just in Custer, last week in my Seneca!!! We weren't towing, but she did 'ok'. I don't think I got below 55 on the hills unless I wanted to. For me, going down the hills is where the Seneca shines over the gassers. I flip on the engine break and relax!!! -Funny enough: I don't see too many Senecas out on the road, so I was pretty shocked to see what I was camping next to at Mt. Rushmore
I'm with LSA376 that a slight tune might alleviate a lot of our power cravings. But like a lot of others, I'm worried that the Allison or the cooling would be adversely affected.
On our trip to Mammoth Cave in Central Kentucky towing a 20' enclosed 8000# plus full provisions, I was down in the 40's a LOT and the cooling fan was constantly running. She definitely seemed to labor up those hills, but I'm also 100% certain we were overloaded. With that being said, I still got 8mpg... So, there's that... LOL
'14 Jayco Seneca 37fs
20' Look Enclosed Trailer