wierd problem, please help
hey guys, so i just got a new(used) engine put into the car, and now the car is running hot on the freeway. around town it has no issues, but on the freeway, if i hold the speed, it starts getting really hot, this happens at any speed over 45-50. the check engine light also came on today and has a code of p0171 any sugestions what could be causing this? also, the shop installed a new thermostat and water pump on the new engine. thanks again.