So you used to have an R9 280X, and now you have a GTX 770 4GB? They are both good cards. The GTX 770 has more VRAM that is clocked higher, and the R9 280X has a larger memory interface (384-bit vs. 256-bit). That's not too big of a deal, though.
I would rather have the GTX 770, myself. It uses less power, makes less noise, and generates less heat.
If you are unhappy with the performance of the R9 280x, then it's just a matter of uninstalling the AMD drivers and the card and then reinstalling the GTX770 and the NVidia drivers.