I never use "packaged stew meat" since you are getting a mixture of all kinds of "Schriem" from the butcher or should I say you really don't know what you're getting. Most of the time they cut up tough meat. You must use a marble textured (fatty) meat, such as Flanken or a Marbelized Chuck. That will solve your problem! Let me know the results. Have a good Shabbos and Enjoy

PS - The sauteing of the meat adds a better taste to the chulent.