Improving consistency at TF2 - How?

I have over 1000 hours of playtime. Been playing for going on 12 years now.

It’s rare I top score on pubs. I know comp helps push you to be better, but due to my job, I can’t commit to any type of comp setting (long, inconsistent hours)

I hop on TF2 for the first time in a while, and any class I play, I absolutely dominate with. Massive killstreaks for about an hour.

After that, it fades back to mediocrity. I co time playing for a couple months, and my match KD can range from 61-20 to 5-20.

I’m not sure the best way to improve consistency.