Wheel out of round?

Well I got myself a heavy duty rear wheel online and have finally gotten it mounted and my ride is now running. However at about 14 - 15 mph I start getting this rhythmic bouncing from the rear. I assume it is just that my tire or wheel are out of round but I thought I would put this before the panel to get some ideas before I tear it down and take it to a bike shop for truing. So I await your wisdom!

__________________
If it can't be broken I'll find a way!

-and-

I'm not lost, I'm exploring!

You can true it your self just go slow it's not hard to do but it does take time or it did for me.Make your self a truing stand or buy your self one they are cheap in the long run can save you a lot of money but can give you a headache too.Good luck if you try doing it your self.But then again it want cost much to have it done either. lol

make sure you put the sprocket centered or you will get a wobble and shaking.
you said you got a new wheel,are you sure you didnt hurry to put the new one on,you might want to recheck your work and adjust a few things,like your chain.

Hi Fin
I would prop up the rear and spin the wheel to see what it is doing. Get back to us with info...POPS