Not knowing what images turn you on, I'd probably say trade in 3 of your four lenses, keeping the 18 -135, and buy a lens with better optics. The 100mm f/2.8 IS L Macro lens would be terrific if you like to do close-up photography. The 70-200 f/4 IS L lens is a lens that will give you great images that you 70-300 just can't provide. Consider the 100-400 IS L lens that has provided professionals the ability to capture great images from a distance. Those are just 3 ideas. I can't tell you which lens to pick but I can tell you "PUT YOUR MONEY INTO OPTICS AND NOT CAMERA BODIES!" I am a pro and I do not sell equipment.

As a wildlife photographer, I must agree with Swamp-gator. Learn how to control your camera and you'll find you're asking fewer questions. It's not that difficult. As an example, 1/500 will barely stop people rapidly dancing or running. Using that info, if the pups are in the sunshine and you have your ISO set at 250, by using the "sunny 16 rule," your exposure will be a 1/500 @ f/11 or 1/1000 @ f/8. Both give you the same exposure. Point is since you are using, or should be using digital, you can see your results IMMEDIATELY and make any corrections necessary. Attached is an example of 1/500.
As Swamp-gator implied, learn to control your camera and you'll be a much better photographer. If you're not familiar with the "sunny 16 rule" it simply says "in sunlight (the subject) the exposure is 1/ISO (shutter speed) @ f/16 or any equivalent.

Dancing people