I'm sorry, hands on testing and analysis will be needed to know what's going on. I can't tell from your description if it's an engine performance or transmission performance issue, or even a problem in another vehicle system. A trained technician can help.
Use this link to find some shops near you that can help with your concern:
www.repairpal.com/repair-shops
RepairPal Certified shops can diagnose and repair your 2014 Buick Verano. They provide transparent pricing with a minimum 12-month or 12,000-mile warranty on repairs and services.