Hey bro,
I too am on a test/deca cycle and I use prami. From what I've read about letro, it shouldn't be used as a preventative for prolactin sides from the deca. Letro will crash your estro levels pretty quick, its some strong shit. The general use for letro is to reverse gyno once it appears.
As far as dosing, the average dose of prami is .25mg ed. I recommend taking it before bed because some people experience some nausea and lethargy until their body adjusts.
I didn't see you mention an Aromatase inhibitor (AI) for the test like aromasin or adex, are you taking something for the possible test sides?