A lot of mods from 1.7.3 are broken, so if you have major bugs and issues, I would go through your list and see which ones are not yet updated for 1.8. I couldn't tell you off the top of my head, but I would definitely check. I have not yet run into any major bugs with 1.8 stock, so I believe your bugs may be associated with the mods.
Also, the terrain shaders slider is separate from the terrain quality slider. See below:
KSACheese's post in 1.8 Terrain. How do I get it? was marked as the answer