What are your Specs? i5 3570k , 8gb ram , gtx 650
When you click F3 in game what FPS does it say ( walk around for a few mins and tell me the average range) ? 80-90
got V-Sync turned on? no
What Setting are you using in mine craft?
Graphics: Fancy or fast
Render Distance: Tiny, Normal short, Far?
Full screen? Off
Smooth lighting? max
Advanced open Gl? On