If I drive the car very conservative when first started cold and especially when going uphill it will slip a bit from 2nd to 3rd when shifting. After 1-2 shifts and the trans warms it is fine. If I drive it soft enough on an uphill and let up a bit while the 2nd to 3rd shift happens it will free spin some. It is out of warranty so that is of the table. Are there any adjustments or mods that can firm up a single shift being the 2nd to 3rd shift?

 

You can get the pressure switches replaced, and also replace the tranny fluid.

 

Here you go:

https://acurazine.com/forums/3g-tl-2004-2008-93/110-diy-guide-replacing-3rd-4th-gear-pressure-switch-3g-tl-2004-2006-a-729149/

 

I replaced the pressure switches 3 weeks ago. Also change filter and fluid. Helped a bit but still flares 2nd to 3rd very predictable.

 

Hmm...I don't know what else to say.

 

Hope your tranny is ok

 

What year, how many miles on the car and has the trans fluid been changed before?

 

If it's on the hills only, it could be the grade logic Honda uses. The programming on the TL trans is one of the worst I've seen, it's flat out horrible.

What fluid did you use? Z1 doesn't have very good cold shifting properties. I had 14k miles on my TL-S and the cold shifts sucked already, with that low mileage. Very slow, long, and sloppy shifts in the cold. I dumped Z1 and replaced it with Redline D4, the difference in cold shifts is pretty dramatic. It also firmed up all the shifts, faster and more precise.