Put the chuck roast into a large, resealable plastic bag.
In a measuring glass, add the orange juice, lemon juice, lime juice, garlic cloves, oregano, and jalapenos. Whisk.
Add the liquid to the plastic bag with the chuck roast then add the diced tomatoes. Close and seal the plastic bag, shake and rub the marinade around the roast then place in a container (just to make sure if it leaks, it doesn't leak all over your fridge) and place in the refrigerator overnight or at least 8 hours.
After marinading, add everything in the plastic bag into the slow cooker and cook on low for 8 hours.
Shred chuck roast then with a slotted spoon, scoop out beef and place in a thin layer on a large baking sheet covered with foil. Keep the liquid.
Broil in the oven on high for 7-10 minutes (watching it carefully). This step is optional but I love the crispy burnt edges it gives and really brings out the flavor!
Serve shredded beef over white rice and spoon extra liquid on top.