At the risk of repeating several comments...
- I did the CDV replacement with a dummy valve (funny, my indy mechanic was fooled and said 'you should take that out'.)
- I put in some really high-end trans fluid during my total fluid replacement upon purchase (not going to get into a brand debate, do your research and choose the best you can, i.e. Royal Purple or the like)
- I replaced the bushings with Rogue products
- I installed the longer clutch stop (I recently posted my experiences)
All are common mods/swaps and each improved the shifting. Frankly, the clutch stop had the most dramatic effect - look at the order I did things in and draw your own conclusions.
Now, as far as technique goes, until the car warms up a bit, I short shift into second at around 3000 rpm. No shudder, no grind, smooth as goose poop.
After I see some heat on the temp gauge, I shift above 5000 and often above 6000. Again, all smooth as goose poop.
I have found that adding a little gas as I re-engage the clutch makes the sport mode (especially) a real joy. So does shifting over 6000 generally.
Yes, it sounds like the Batmobile turbine at that speed but if I wanted a quiet car I would have bought a Prius.
If I had to choose one thing it would be the clutch stop. The thing I'd drop from the list first is the bushings - but even though the improvement was subtle for street performance there was an improvement. But my list is pretty inexpensive so I did it all.
inTgr8r - After a brief but enjoyable early career driving big rigs and dump trucks (15 speed in one and 5 & 4 in the other) I nearly always double clutch... especially downshifting.
Nothing new here, I suppose. But perhaps this provides some confirmation of some really good ideas posted above.
Carry on.