My tranny grinds when i switch into fourth and then also in fifth but only when it is in a high RPM. What can I do to solve this. Don't really think that my tranny is bad. Just bought the car like 8 months ago. could my clutch slipping be the cause of that cause my clutch needs to be replaced?

 

if your clutch is slipping, replace it. It's most likely the source of your ills, but...

check to make sure the clutch master cylinder is in good condition and has enough brake fluid in it, bleed the line if need be, its quite simple...
you can bleed it yourself if you buy a speed bleeder.