According to your Nissan's maintenance guide, coolant and spark plugs should be replaced at 105,000 miles during "normal" driving conditions.
Use this link to find some shops near you that can help further:
www.repairpal.com/repair-shops
RepairPal Certified shops can diagnose and repair your 2012 Nissan Frontier. They provide transparent pricing with a minimum 12-month or 12,000-mile warranty on repairs and services.