How to check for previous "tuner" on a used truck?

My own experience.

My 08 6.4 developed a bad #8 injector at 4 years 9 months and 65,000 miles. I took my Hypertech out (lowest setting) and took it in.

Covered under warranty. No costs, no issues.

Maybe they couldn't detect the previous Hypertech.
Maybe it didn't matter if they did as it had no bearing on the failure.

Don't know, don't care. They covered it.