Mammajamma

Okay so I have a 2002 chevy tahoe 5.3 V8. Service engine soon light had been on for a bit and when I got the money to get things I found out it was my knock sensors, I had my mechanic replace them, the gaskets, and spark plugs. He built the wall so water hopefully won't rust out the new knock sensors. My service engine light came back on so I had him replace the knock senor wiring harness, I got it back and it came back on. He kept it for a couple days and could not figure it out. Every time he put it on the computer it said knock senors 1 and 2. After replacing all of the knock sensor stuff it started to idle hard. I took it to a dealership had them go through it. They said replace the ecm, they wanted 700 to do it. I had already done 1500 in repairs in less then a month so I could not afford that much. My mechanic found a GM certified mechanic that would do it at his shop. We also have replace the MAP sensor by now. Got the ecm replaced and the mechanic drove it for 60 miles and it came back on. We called the dealership we got the go around and what not and they said it could be the iac sensor. I replaced that my self and it was running great. Idling a little rough still but better. After driving 45 miles the light came back on and now we are getting the knock senor code, fuel composition sensor and a coil miss firing. I am honestly tired of replacing sensor and things the dealership thinks it is and chevy says because of the year and miles on it they can't do anything about it. Has anyone else had this issue if so what fixed it l?