I see the problem.
He didnt use the proper oil. The oil recommended in the USA is 10w30 but that's not enough for jdm power plants. You must use 15w40 diesel motor oil or your engine will prematurely wear like it did in your car. The LS doesn't not have a vtec lobe. Don't listen to these Pollocks. When the LS engine engages lean burn at 2000rpm, regular motor oil is too thin at operating temp and doesn't properly lube the camshafts. That's why you need heavyweight diesel motor oil like japan originally intended.
I highly suggest fixing your regimen.