Judging from your replay, use paddle shifter for gtr cars. You are shifting wayyy too slow, clutch is in too much. When downshifting, get it in gear and get the clutch out, you don't wanna be dilly dallying with the clutch in trying to corner your already narrow turns. THe reason why your rear wheels lock is because you let the revs drop by keeping the clutch in. you wanna break, clutch in, do a little heal toe/double clutch, drop it down the gears until you are in the one you want to be during the EXIT. turn in,hit the apex, already be accelerating, start shifting up. But yea, your shifts are way to slow anyway. Other than that, look for a wider line through turns, go to the outside edge and turn in from there. You want BIG radius turns. After that, do it as many times as you can until your fingers or feet fall off. Then you'll have it down.