Getting all my pieces together and it’s coming to pulley and belt selection. I wanna go fast but I also need to be able to go up steeper hills. I’ll be running 12s on 6374 190kv motors. Any help is appreciated.
Plug all your info into this calculator and play around with pulley sizes until you get a speed and hill climbing ability you like.
What wheel hubs do you have?
Rockstar pros
I don’t see anything about hill percent on that calculator
Dual 6374 will pretty much take you up any hill. 
See what available pulleys for your hubs and go from there
Everything from 60 to 80 tooth hubs. I got a 16 for the spur gear
16 70 gives a loaded mph of 40. I was thinking of going with that.
Right you are! Sorry, there are several esk8 calculators out there and I just picked the first one that came to mind. The one I remember having grade calculation isn’t up anymore. My last build (dual 6355s, 10s, 40A battery each side and 65A each motor, 15:60 and 6" wheels, ~26MPH) could handle every hill I threw at it, no problems.