Nice truck! That is going to be my next truck.
My truck has the GM rake but with the tt hooked up it sits level and tows great. If I leveled it I would likely need air bags since my tt will squat the rear almost 2-3". I would say go for the level truck if you don't squat much with the trailer hooked.
I would also run the stock tires for a little bit then see how things go. I would definitely get the different tires but see how things ride first with the stock size rims. You might want the 18" rims with a little larger tires for more sidewall?
As for the speedo, the dealer might be able to do that?
Enjoy.
