i'm trying to figure out how to make this library sustain the sound when i repeat the notes, if i press the sustain pedal of my midi controller the notes begin to overlap each other and makes a giant bass mud...

someone knows how to do it?

 

I don't use that library but perhaps the sustain pedal activates some kind of "polyphonic mode" keyswitch.
In Shreddage and most guitar libraries Sustain is just another articulation, usually the default one. You can activate it with a "MIDI note" keyswitch but also a MIDI CC.

 

In the manual, about Fretting Controls: