I did what you did in 2012 while out west. I went up a long 10% grade and was down to 20 mph with my 340hp. A GPS with grade info. would be great, but I do not have one. Instead, I bought the Mountain Directory.
Mountain Driving Guide for Truckers, RV and Motorhome Drivers
I also have Allstays Camp and RV, and also Allstays Truck and Travel apps on my I-Pad. These apps give grades, Walmarts, fuel locations and a lot more. The Mountain directory says that the steepest grades are in the East.
Will be interested in anything that you find out about the engine chip mod.