I browned the cubed chuck on the stovetop then braised at 250 degrees for two and a half hours.
Is this ailing dish for dinner tonight?
Need some more info before diagnosing the patient.
Is the beef tough and dry, or tough like not cooked through?
Did you cook it covered in the oven?
Did the liquids reduces a lot? (they shouldn't have)
Is your oven inside temp true to the outside dial? (could you have overcooked it?)
Is this the recipe you made?
If not, which recipe or what was different?
Don't despair...the dish is probably recoverable.
I find that beef goes from tough to tender at 'some magical point not well defined by a recipe cooking time" . Cook it some more until it hits that point.
I agree with Sam. My daughter called me last night because she thought she overcooked her beef braise. She let it go another 30 minutes and it was perfect. Have you checked your oven temp for accuracy? Mine is 25 degrees off.
Forget the clock. Cook it until it is done.