Trim any excess fat off the flank steak or sirloin. Freeze the meat for about 1-2 hours until it is firm but not frozen solid.

Use a sharp knife to cut the meat into thin strips, about 1/4 inch thick, cutting against the grain for tenderness.

In a bowl, combine Dr. Pepper, Worcestershire sauce, soy sauce, brown sugar, garlic powder, onion powder, black pepper, and chopped jalapeños. Mix until the sugar is dissolved.

Place the sliced beef in a resealable plastic bag or shallow dish and pour the marinade over the meat, ensuring each piece is coated. Seal the bag and refrigerate for at least 4 hours or overnight.

If using a dehydrator, preheat it to 160°F (70°C). For oven-drying, preheat your oven to its lowest setting, usually around 170°F (75°C).

After marinating, remove the beef from the marinade and pat dry with paper towels.

Lay the beef slices in a single layer on dehydrator trays or a baking sheet lined with parchment paper.

Dry the jerky in the dehydrator for about 6 to 8 hours or bake in the oven for 4 to 6 hours, flipping halfway through. The jerky should be dry but still slightly pliable.

Once done, let the jerky cool and store it in an airtight container or resealable bag.