Big_BlueSierra

2017 Sierra 1500 SLT, 5.3 Hi guys, I really need help at this point. Ever since I got my truck back from the dealer, it has been noticeably louder. It went t0 the dealer for a new Torque converter. I'm not sure if it's been this loud and I just forgot after being without it for two months (it went in on January 6th, got it back around the end of February), or if I'm just nitpicking it. I have these three codes p0451, p0174 and p0171 At the dealer's recommendation, the MAF was changed, my tank pressure switch/sensor was changed, the purge valve on the motor was changed, the throttle body was cleaned, New air filter was installed (needed that one). It got a new fuel pump back in January during the freeze, and I didn't have these codes until a week ago. They even disconnected the battery to hard reset it and they came back almost instantly after running for a minute. At this point I feel like they are throwing parts at it and trying to see what sticks It was taken to another dealer for a second opinion, but they want to keep it and told me it would be an estimated 3 month turn around because they are backed up. I don't doubt, but a 3 month turn around, no thanks. So I'm turning to you guys for help as the other non-dealerships around here are basically chop shops, and our only good one has a long turn around as well. What can be causing those three codes? They pop up together no matter what. I have not noticed anything different, aside from a delay on acceleration sometimes but it's so few and far between that you really have to watch and wait and you can't make it do it. They are now saying it's the purge valve canister that sits under the truck and connects to the fuel tank but are also saying they can't guarantee that will turn the codes off