I've started grinding 3rd gear at low speeds. By low I mean shifting into third at around 15-20mph. Today it did it with 5th as well, first time.

Shifts fine, engages fine.

Should I be expecting a new transmission soon?

For reference, car made 219rwhp at 12.5psi, it was recently turned up to 14psi.

 

What kind of trans oil are you using? Have you ever checked the level or changed it?

 

Yes, it was changed about 2 months ago.

Using 75w-90 dino oil (Don't remember which one)

 

up shift or down shift?

 

Up shift.

 

5 speed + power = problems. just one of these things you have to get used to.

get some atf and fill your trans up, drive it maybe 5 mins or on jack stands leave it in gear idling for 15 mins, you just want to get the gears nice and covered and the atf moving, drain then fill up with amsoil. did that with my 5 speed when i bot my 99 and have not had any problems since and ever is surprised the 5 speed hasn't failed at ~250hp 225ftlb.

also cold oil makes my DD do that in all gears shifting under 2.5-3k

 

+1 mine doesn't like the cold much either. And I'm in Florida. The op is in Minnesota!

Does it work better hot?

 

My 6-spd makes so low griding noises in low rpm up-shifts when the trans fluid is cold

 

3rd gear grind is common. Seems to be the weak synchro of the bunch. Just baby 3rd a little and maybe consider upgrading from the dino juice you put in. I know AMS oil MTL is the hot ticket for 6 speeds. Is it also the best stuff for 5's?