Big problem with LGT is that it simply doesn't stand up under scrutiny. Many of the so called proof texts are in the Greek subjunctive or even the optative mood. I understand this to be an aspiration or a hope, rather than a certainty of attainment. "May you live forever" is an example of these moods. "Merry Christmas" is another. The holidays are a bummer for some, regardless of the good wishes.
It's certainly true that, eventually, the redeemed will attain a state of sinless perfection but it won't be in this life. Augustine gave a lot of thought to this doctrine, in works such as "On Man's Perfection in Righteousness." His "Writings Against the Pelagians" include discussions of this topic. If someone would like to set forth some texts that "prove" sinless perfection, I'd like to examine them.