What would cause it to surge after it got hot and you was driving

Hello, I'm not sure of the question. Sounds like your vehicle is overheating especially when you're getting up to 45 - 50 miles per hour and more? If this is the case, I'd be checking the cooling system for leaks, for a possible thermostat that could be not opening fully, or some other kind of coolant circulation issue. Check for debris in front of the radiator possibly blocking air flow. Use this link to find some shops near you that can help with your concern: www.repairpal.com/repair-shops