highway vibration

when i took the engine to the machine shop when i got it. it was horribly out of ballance so the guy used the b&m flex plate and found out there was a 318 balancer and told me that he could balance every thing with what i had and it ended up being a pound out of weight over all so he added weight to different places and took weight out of a couple of places on the balancer but the car was driving perfectly fine for the first few months i have just now started having the weird vibrations