Heat oil in a large skillet over high heat.
While oil is heating, place 2 tablespoons flour in a large baggie; add the chicken pieces one at a time and shake to coat chicken with flour. Set aside on a plate.
Add chicken to hot oil, skin side down, and sauté until golden brown, around 3 to 4 minutes. Flip over and cook other side for 3 minutes. Remove chicken from heat and set aside.
Turn temperature down to medium and add chopped onions. Cook, stirring occasionally, just until soft. Transfer to slow cooker. Stir in paprika.
Place chicken broth in a 1 cup measuring cup. Add reserved tomato juice to make 1 cup liquid. Stir into onion mixture. Add diced tomatoes, yellow pepper and salt. Nestle chicken pieces in sauce. Place lid on slow cooker and cook on low for 6 to 8 hours, or until chicken is very tender.
Remove chicken pieces from sauce and set aside, leaving the sauce in the pan.
Place 3/4 cup sour cream in a small mixing bowl; whisk in remaining 2 tablespoons flour. Whisk in 3 spoonfuls of the sauce from the chicken, one spoonful at a time. Stir mixture into sauce in the pan and simmer for 3 to 4 minutes.
Season to taste with salt and pepper. If desired, add more sour cream to taste. Place chicken back in sauce to heat through.
Serve over Hungarian Dumplings, egg noodles or other pasta.