Can't shift into 6th
 

I was racing this built talon and I was ahead:) but i went to shift into 4th and it ground on me. Not to big of a deal it does that with like 90k on it. So I found 4th shifted into 5th and it was tight and hard to shift. So I beat the Talon but I cant shift into 6th now it just grinds like crazy. All other gears work includung Reverse. I was driving home and pulled it out of 5th and the shifter got really stiff. I was able to find all gears but 6th they were just hard to get in. Then it loosened up after a few gear changes. Car is a full weight 2001 WS6 with a monster stage 4, 475ish at the wheels. what could it be?

fork pads.
take it out and go through it.

do you think that is it or could it be the 5-6 keys?

It could be either. No matter what it still has to come apart to fix it. I'd put billet keys, bronze pads and carbon rings in it if you are gonna pull it apart yourself. I am 100% sure you are going to find more damaged in there besides the 5th/6th related parts.