Note on servings and meat selection: You need a fatty cut such as chuck. It should be well marbled and may have a fat cap or other larger pieces of fat. Your butcher can help you select one. With a fatty cut of meat like this that will be roasted and reduced I plan on about 1/2 pound per person (raw weight). If I want to serve six, I buy a 3 pound piece of beef. That being said, my husband came home starving one night and ate most of a 3 pound roast the first time I made it. I was rather surprised, even for him that is a large meal.
Place meat in the bottom of a large crock pot. If there is fat cap on one side place it up so the fat can run down and baste the meat.
In a medium mixing bowl, whisk together water, brown gravy mix, ranch mix, Italian dressing mix, and black pepper.
Pour the mixture over the roast and turn the crock pot on low. for about 5-6 hours. The meat is done when it is no longer at all rubbery. It will be so tender that when you poke it with a fork chunks will just fall off.
DISCLAIMER: Remember that all crock pots have different cooking times! I have a medium pot that I used for a 3 pound piece that took over 7 hours. In my larger crock pot I was done at 6 hours. If you don't check the meat every so often it can easily be overcooked and thus ruined. I suggest checking at two hours and then every hour or so after that. When the meat is close to being done it is best to check every 30 minutes.
To make gravy: Measure two cups of the hot sauce out of the crock pot. Pour about 1/2 cup in a medium sauce pan over medium heat.
Whisk in the flour until no lumps remain. Gradually add in the rest of the two cups of hot sauce, whisking through each addition until it is all incorporated. Continue to whisk until the mixture is thickened. Taste for salt and pepper, adjust as needed. Serve with the roast.