Frame-rate drop in 14w28b

I am getting horrible frame rate in my single player world. i usually get between 50-80 frps at my base but in this version the frame rate was going into the 30s. The nether has the same problem i usually get 100 frps there easy but it was doing not even half that. The only reason I can find for this is when you press F3 in the upper part the C (which i suppose is chunks) says C: 3400/8464 and that number kept on rising. For me it usually stays in the 800s/8464. I know this isn't my computers problem because i downgraded to 14w27b and it was fine