Is it throwing codes? The SYN amps have a built in micro processor that will blink the LED's telling you if it sees a short, repeated short thermal issues, under voltage, over voltage or DC offset. http://www.wetsounds.com/media/products/SYN2/Syn2-4_Manual.pdf
See what is happening when the amp cuts off. It will tell you whats going on, count the blinks on the LED. It will blink one time and pause and then 1,2,3,4,5 times more. Codes are 11,12,13,14,15.
Once you see what code it is doing, then you can see if it truly is the amp or something else. A shorted speaker, cut in the wire shorting out, voltage issue etc..
Give Gyver a call at the office at 877-938-7757 once you count the codes and he can help you trace out the issue.