I have an 2009 GMC Sierra extended cab long bed. It’s completely stock bought it recently at 197000 and it’s only at 199k. I bought it and the first week ran like a beast. It was quick compared to my old gasser. Then I started noticing lack of power and low mpg. Then the efr code popped up and got the dealer to pay most of the cost since I only had it for two weeks. We’ll the guy that fixed it did something wrong. And it was a plane the dealer sent the truck too. Now there’s a air leak or boost leak I’m not sure. But it’s an insane whining noise everytime I hit the gas. And it’s not accelerating as it should or the turbos not spooling right. And there’s almost no low end power. So I took it back and the mechanic had the balls to say that’s how it supposed to sound since the egr was clogged. I told him it ran better when it was clogged. I’m asking for advice in what I should do to diagnose and fix what happened when the egr and cooler were replaced. My truck is like an annoying whining slug at this point lol. All advice is greatly appreciated!!