Dude, you just need the practice. I had the EXACT same problem as you, but a few weeks later it's all good, and i don't buck the car at all any more.
You just need to be sure you reach a higher RPM before you shift while in lower gears.
The first 3 gears have a lot of torque, especially in the Z, shifting while under 2000 rpms will cause the next gear to have to overcompensate thus resulting in the bucking effect.

 

its your technique trust us


We got this car as my girls first EVER stick car. She had driven my heads cam stang a few time for practice. I spent 3 weeks teaching her to drive in this car and she started out with the condition you explained. with me behind the wheel, smooth as galss. She drives the car like a champ now.

 

If your clutch engagement point is as high as most Z's, make sure you are more than half-way off the clutch before pressing the gas. Oh, and if you've never driven throttle by wire, it is much more sensitive than a cable.

Electricity travels faster than the slack on a hard line. So if you give it a little too much gas before engaging the clutch enough, it will 'buck' when you release the clutch all the way. This can happen at any rpm, and very quickly too.

Drive with your left foot on the dead pedal, and lift if up and bring it over for every shift. As soon as you touch the clutch, it starts to slip. Always, always, always press the clutch ALL THE WAY DOWN!! I've seen thread posts where people say they only press the clutch 1/2-way, and then we started hearing about tranny problems. Coincidence? I'm surprised that Nissan actually backed that one up under warranty.

 

+1 . great thread