no sustain in garage band

Using iRig... Guitar plugged into computer. When I try to play a rhythm longer than 3 secs, the volume cuts on the guitar and it starts to sound thin, and sustain almost non existent.

Ive tried turning the noise gate off.

Ive tried my guitar through my amps to see if there is a guitar issue. nope.

Ive tried using the sustain pedal in Garage band... nope.

what gives? Is there a solution... please tell me there is... It would make my life a lot easier.