Slow singleplayer tick speed

So my PC Specs may not be the best but i'v discovered that before the update 1.7 I had no problems with the 20 tick/sec, but now I get like tick lags where the sun lags back, days take 10 minutes longer than they should and animals move slow. And I did try this in a 1.2.5 created map with the 1.8.8 update and it still did that so its not because of the new biomes that came in the 1.7 update. I have no idea why my tick speed is slowing down, did you guys change something when it comes to how ticks work in 1.7?