Pmac he testified at trial how could he not be a rat?

His argument was that he did not turn on certain people in the family.

He did not give up Perscio his father his crew.

He testified and gave up associates

His deal was similar to Sammy the Bulls, in the sense Sammy did not give up anyone in his crew.

It makes no sense to me either

They had to have something on him...

They probably said you are looking at another 10+

He probably tried to buy his way out and said I cannot testify against certain guys because it would put my fathers life in jeopardy

I think he reached out to Persico through messengers said I am not going to hurt you and anyone that is dear to you. He probably sent him some nice money behind the scenes

And said please leave me alone
I will disappear

Remember back then Persico killed a D.A. or ordered the hit and they killed the father of the D.A. by accident.
Back then the Colombo's killed a cop

The Colombo's would kill anyone

When Sammy flipped Gotti send him a message a Son for a Son
Meaning leave Jr. out of it and I will not kill your son.

Gravano stuck to the deal and so did Gotti.

Gravano did not testify against his crew and Jr.