I noticed this started happening around the same time my clutch started to slip. I used to bang 3rd all the time and it would grab hard without anything harsh happening. Now I don't even have to bang the gear and it would still grind. This only happens when i shift at redline or near redline.

I have 110k on the original clutch and tranny. All i have done is intake/ypipe. This also happens to my friends 96 5speed with i/cb. He changed the clutch at 80k miles. He now has 89k miles.
-Paul

 

Everytime I have had my clutch go (like 4 times, I have a wet clutch). It has done some minor damage to the synchros. Last time I lost second over about 6000 and it grinded from 4000-6000. That was a lot of fun. I would be willing to bet you have a worn synchro.