I just sold my 2014…
I just sold my 2014 Silverado with the 5.3 and 6L80 transmission. It was 5000 miles short of 300,000 miles. It was a great truck overall. The only things I did to the engine were to replace the high pressure fuel pump under the intake and replace the thermostat. At 100,000 I had a tuner reprogram it. The estimate from ho tuners was 425hp. It was immediately noticable. I won't lie it was quick. Not many trucks could touch it, with the exception of the viper powered dodge I ran up on. He laughed at me.
The major issue I had was the 6L80. It went out at 130,000 I had it remanufactured. It went again at 230k and the third was quick at 250k I went to a friend who builds transmissions every day. I told him to treat it like it was his. I never asked what he did differently besides the torque converter. It was strong when I sold it. I never changed a thing under the hood for performance parts. I was stayed on top of the oil changed. Yes I used the onboard monitor. I stuck with 0w20 synthetic by mobile 1 with wix filters. Btw I still got 22 mpg.
Jaded by the transmission issues I bought a 2024 RAM with the 5.7 and 8 speed. Even with 300k I'll bet the Silverado will still smoke it.