My ribs this year turned out tough but not dry in the oven, opinions?

Hey all, so last year my sister taught me how to make some pretty great ribs in the oven, but this year we had to buy a new oven and we also used a bigger cookie sheet to put all 3 racks on one sheet versus usually one or two on one sheet, so those were the changes. For the loin back ribs last year we were seeing success at 290 degrees for about 2 and a half hours with at most 2 racks of ribs on one cookie sheet, tightly sealed with aluminum foil. At the end we put them on the grill and put all the BBQ sauce on, and all that turned out fine, just the meat was kind of tough rather than dry. It's still pretty good and edible, but not something we want to serve up with company. Would anyone have an idea on what to modify to get a better result? Most signs point to being undercooked, but i don't want to go too far in any direction without reaching out for opinions, thanks all! submitted by /u/goldenpp72