2004 Mercury Mountaineer Rough Idle

Okay, I am at wits end with these issues. And am getting tired of driving my truck an hour to the shop every week. A little backstory. We bought our truck and after a little over a month the motor went out. Bout a new motor not used back in July. In November that motor went out (was loosing oil pressure) warranty put another new engine in it. We picked it up and the check engine light came on said Bank 1 Sensor 1 (o2 sensor) so they got the part and replaced it. Then after they did that they told me my passenger valve cover was cracked and leaking ( it wasn't leaking prior to the new engine and it was a week after the new engine was put in ) Ford only part had to order it. Last Friday they put the new cover on (mind you it ran fine and smooth like a good truck should during the few weeks before the valve cover) Drove it home Friday night, Saturday morning started up the truck and smelled gas, Checked under the truck had gas pouring out. Popped the hood and my fuel rail on the passenger side was off injector 2 leaking out major. Towed it down to them again. Got a call on Monday afternoon, told me the injector broke at the lip and wouldn't stay locked. (There fault so they replaced it) Picked it up and it was idling rough when I stopped, no fault codes. Christmas day it pooped up with a code P0171 Lean condition (Confirmed) and P0302 Misfire (pending) Called them yesterday and was told the injector was used and it might be dirty or sticking, and to just keep driving it and it might clear up. Now I am concerned that I am going to damage the engine by playing there game. And curious on what I should do.