Clutch and 3rd Gear problems.....Please help

I have a 1999 Cobra and whenever i race and try to shift into the third gear it gets stuck and i have to pull the shifter back and then it would go into 3rd and it only does it at high speeds it shifts really smooth when u drive normal. Is there anything that i can do to fix this problem???.....This is what happend to me tonight i was racing this 1995 Formula V8 6spd, and i pulled away in first and second gear and it wouldnt go into third gear so i would lose every time...and one time we went around and raced again and when i got up to 60 or 70mph in second gear i tried to shift into third and my freakin gear went into first instead of 3rd... ....i basically burned my cluch which brings up another question.......I am not sure what kind of clutch i should get, but lets just say that happens again i want a clutch thats not gone burn that easily....please guys help me decide what to do i appreaciate any suggestions...

But how come when i drive normal it shifts very smooth ??? I mean i am not really an expert when it comes to transmissions but i should be able to tell if it was toasted....

Well lets say the 3rd gear synchro is out, what do i do and how much does it cost to fix??? And my transmission doesnt grind, it slipps when i put it in first and try to accelerate same with the reverse gear....once i get going there is no problem, but tonight when i was driving home from work my clutch got very stiff and it was hard to push it down and my transmission was making whining noises some people told me my clutch is toasted...i have difficulties to accelarate basically i am just sittin there at the light and it takes me 30 seconds to get rolling lol.....i parked the car in the garage and i am not moving it until its fixed...

Hey man thanks alot i appreciate your help.....