Find a tire store that can ROAD FORCE balance your tires, usually with a Hunter machine. Prices for this service vary all over the map, but it's worth it. They'll match up the heavy side of the tire with the light spot of your rim, and then they'll put a force on the whole rotating assembly and balance from there. This is as good as it gets.
I'd swap wheels front to back, one side at a time, to confirm that it's one of the front tires and which one it is. If it goes away by putting it on the back, get the tire shop to re-balance or replace the bad tire.
I recently had new tires put on my 2500HD. I went with Toyo Open Country A/Ts. I don't drive on the freeway much so it was about two weeks before I drove on the freeway. Anyways,I get a slight vibration in the steering wheel at speeds over 45mph. It doesn't get any worse at higher speeds. Its like a switch gets flipped,at less than 45 theres nothing,past 45 and I get the vibration.
The tires were balanced when installed and then again a week ago. The vibration got better after the second balancing but its not gone.
I'm thinking its a bad tire/tires. I didn't have any vibration with the old tires. I haven't hit anything that would have bent a wheel or changed the alignment.
What else should I be looking at?
yes it sounds like a tire may have some excessive road force, but if the vibration is still there you may need to look into worn chassis parts.
usually vibrations that are tire-related don't start till after 55 mph.