Ox accuracy suffering. Thoughts? Ideas?

I've been running my ox now fairly hard for around 6 months 3 to 5 nights a week. First issue I was having as loose pulleys. Problem solved. It continued to run very well up until recently. It has been acting up and I haven't quite tracked down the problem. Hopefully someone can help.

My OX is plain-Jane just a little bigger 1500X1500
Gecko G540
Mach3
cheap ebay cnc motor kit from Longs-motors(1 amp nema 23, 1.8 degree )
power supply that was provided 24V 4.5 Amp
I usually cut from 100 to...

Ox accuracy suffering. Thoughts? Ideas?