I had some questions I searched found a few problems but not like mine.

I have a s4c b16 si tranny

When I punch/smash from 1st to 2nd and then go straight to fith it grinds and don't go in, If I let the rpms go down it goes into gear and dont grind. My reverse is hard to get into most of the time. When I shift normal from 1-5 it's butter. Is this a early sign of my tranny going out.

-new Honda mtf was put in 300 miles ago
-clutch fluid has been flushed and re-bleed with prestone synthetic brake fluid
-pw:Jdm magnetic drain plug

 

Sounds like a worn 5th synchro and sleeve.

 

^^ i replaced both on mine and it still grinds

 

sounds like a worn syncro for sure. Gotta be careful that everything goes back together right or you'll still have problems.
ohsnap did you follow the manual to a T? stuff like the sleeve and hub look almost identical in both directions but there is only 1 right way.

Honda MTF is great stuff if you have a top notch trans, but once it gets warm its thin like water, so for something a little less healthy i like to run a thick oil like Motul 75w90 trans oil.