I am having intermittent issues with my 5th gear. The first time this occurred was 3 months ago, then it happened a few days ago, then it did it again today.

When I am shifting into 5th gear I will suddenly get a gritty and rough feeling through the shifter, sometimes this is accompanied with a grinding noise. I can get it into 5th gear still, but the sensation is concerning.

But the odd thing is that the issue will resolve itself later in the same drive, I will downshift and then go back into 5th and the issue is gone. Both times I remember this happening it occurred during the first shifts into 5th gear of that drive when everything might not be warmed up. This grinding happens with the clutch 100% in, there is no chance this is the result of me letting it out accidently (I checked).

The increasing frequency of this makes me concerned. I replaced my transmission fluid about 1000 miles ago (Redline MT90), the old fluid was very dirty looking. The clutch is likely original, I say likely because I got zero papers with my 4runner and it had 165k on the clock.

Any ideas what the issue might be?