Maybe try balance charging it with a small current. There are a lot of variables and unknowns here, you should try flying it several more times and see if you notice any trends or patterns.
GemFan props are cheaper since they spend less time balancing and calibrating them at the factory. If you want quality props that are actually factory balanced, I think T-Motor makes some of the best. I found this comparison review between GemFan vs. T-Motor Carbon Fiber props...
Hey otisking. If you're a complete noob at building quadcopters I suggest you read up on a few guides first.
Try this for a start: http://quadcopteruniverse.com/pages/introduction-to-selecting-the-right-parts
I think there are a few more articles on that site on motors/escs, may be helpful.