Brown the beef and onion in a skillet for 9 minutes until the beef reaches 160°F, drain the fat, and stir in the cumin and chili powder.
Boil the macaroni in water with 1 teaspoon salt for 3 minutes less than the package directs and drain.
Place the beef, pasta, drained tomatoes, evaporated milk, whole milk and remaining salt in a buttered 6-quart crockpot.
Cook on low for 45 minutes, then stir in the cheddar and pepper Jack by handfuls.
Cook on low for 45 to 60 minutes more until the sauce is smooth and the elbows are tender.