A lot of times when i'm playing Vanilla (Not Feed The Beast or AT Launcher) My chunks constantly don't load and I have to f3 + a to re-load the chunks constantly. I made sure Java was updated and it's still not working. Have you heard of anything in this nature? Really need some help!
This is a very old bug that has been present since, well, forever; at least in multiplayer, affecting singleplayer since 1.3.1 when the client-server merge occurred. One solution that I have seen is to lower the FPS slider (and there is no need to have it set higher than 60 anyway as most monitors can't display more than that, if set to Vsync); when set too high the game doesn't give chunk updates enough priority; lowering render distance also helps for a similar reason (less chunks to update). Also, Optifine with its advanced chunk loading controls may help; I've never experienced this problem while using it while it is frequent in vanilla (most commonly, when flying or in a boat and changing direction; the game seems to "forget" about some chunks, leading to a line of chunks that don't render until you reach them, completely against the normal chunk loading where chunks near the player render first). In fact, if the modded versions you use include Optifine that may explain why you only get it in vanilla.
TheMasterCaver's First World - possibly the most caved-out world in Minecraft history - includes world download.
TheMasterCaver's World - my own version of Minecraft largely based on my views of how the game should have evolved since 1.6.4.
Why do I still play in 1.6.4?
There's my settings. What would be optimal? I'll install optifine later.
For the chunk problem use optifine.