Didn't Sammy Volunteer to testify on his behalf after he tried to kill Sammy ??

I like Gravano's videos, and think he's the most intriguing of them all, and basically think like 70% of what he says is true..30% to puff himself up more...But I think Sammy volunteering to testify for one of his crew against the government makes your radar go up...Why's he doing that ?? Maybe because Carbanaro knew about alot more about what Sammy did then he admitted too