My minecraft is glitching?

My minecraft keeps glitching so where the blocks change to invisible blocks or other random blocks. This happens while I'm using the Faithful32x32 resource pack and TheHunterWolf Pvp pack. (These are the only two I've tried) Today I just deleted my minecraft folder and installed Forge Modloader 1.6.4, Pixelmon 3.0.4, and Optifine 1.7.4. Before today, I've never had this problem. My gamma is set to 1000000.0, and I'm trying to play on us.mcgamer.net