What lens are you using with your camera? It may be worth getting someone to have a look at it if your having issues. As for the first question the Pentax are great cameras and I think they are very much over looked. For the money they are outstanding bits of kit and not much can touch them. If you go by Amazon pricing a K-3 your talking similar money to a Nikon D7100 ( plastic and not ff) and a K-IIs your talking Nikon D5200 (plastic and not ff) pricing. If your sticking at this sort of price point I would see no real need to swap systems. The full frame cameras from Nikon, Cannon and Sony will cost you far more. All the lower end and older model full frame cameras you do sacrifice all sorts of things to go full frame. For example you could get a used D700 for similar money to a new K-3 but the K-3 will have more mega pixels, more dynamic range, more colour depth, faster burst speed, less shutter lag, have video capability and come with a warranty. I think your best to ask your self what you are going to use the camera for and then work from there and see what will work best for you.