my 05 tsx 3rd gear grinds when i shift fast but if i do it slowly it dont grind and sometimes going into reverse most mechanics said its the syncho or the trans so any suggestion lmk

 

Typically grinding in one specific gear is a bad synchronizer, but since your're having a problem with reverse also, you may have a dragging clutch either from a master cylinder problem or a broken piece on the clutch disk. Check the master cylinder reservoir. If it is low, add fluid and check the master cylinder push rod under the dash for leaks.

 

^correct. Check that the clutch pedal does not have excess freeplay. It seems like most TSX clutches engage at a very low pedal position...which makes it difficult to shift fast.

I don't expect that we'll hear back, but....

Is this an aftermarket clutch? What kind?

Check clutch fluid level first. Then bleed the system. Then adjust freeplay properly. Freeplay should be between 0 and about 6mm (1/4").