Could taking two acetaminophen / hydrocodone 750 mg / 7.5 mg lead to shallow breathing and shortness of breath?

Yes: The short answer is yes. Hydro codone is an opioid and one of the significant and serious side effects of this class of medications is respiratory depression. It is vitally important to take all prescription medications only as prescribed by your doctor. If you experience a side effect such as you described, you need to discuss this with your doctor and may need the dosages adjusted.