Re-learning to shift a 13-speed EF

Does it happen in any other gear?

The vgt is variable geometry turbo. A lot guys go back to the old style after a delete but I'd leave it if it's not giving you any trouble. Better spool up on the low end

 

Less turbo lag in the beginning when you're trying to get it spooled up.

 

It just means when you move the button back, you're going into high.

No. The turbo charger is spinning at low engine RPM basically as fast as the engine's exhaust velocity. Once you floor it, a bunch more exhaust is flowing through the turbo, but now it "spools up" (spins faster) because of heat expansion in the exhaust which is 99% of what drives the turbo. Exhaust velocity at that point being a tiny percentage.

Now take a regular turbo with no VGT. It's got a fixed size exhaust housing. The smaller the inside is, the harder the engine can drive the turbo (faster spool up). But smaller also means higher exhaust temps, higher drive pressure (hard on head gaskets). So you want a smaller inside so the turbo gets up to speed faster (spool up), but it sure would be nice to have a larger inside for normal cruising, and long pulls, right?

Enter VGT. It's got vanes inside the exhaust section of the turbo that can make it seem small when you need to build boost quickly (like leaving a stop light), and then the vanes open up and it acts like a big turbo once you have sufficient boost pressure.

Ever watch your boost gauge from a dead stop? It starts building boost kind of slow, then all the sudden it just takes off? VGT is a way to make it spool faster right off the bat.

It also has other uses. Helps warm up your engine faster in the morning. Helps your Jakes work ten times better. It can even be used as a full on exhaust brake on a pickup. It adds some complexity to a turbo, and a lot of cost, but it's a great invention.

 

Perfect description. I hope OP will understand how it works.
I want to add something tangential. The turbo actuator and the vanes that it moves..
The vanes can be easily damaged by very high temperatures.
The actuator won't be able to move them anymore and a fault code will be logged.
There is a solution to this issue. It's called a Turbo blanket. I strongly recommend it's use.
Why Use A Turbo Blanket?
Here is turbo blanket for a Holset VGT:

 

Turbo blanket helps maintain EGT coming from the engine. Heat expansion from the exhaust gas is what drives the turbo, so you want it to stay hot. Too high of EGT's in the first place can be a problem for the turbo. 99% of the time, that's a "too much fuel for your available air" problem. Throwing on a turbo blanket will make a noticeable difference in spool time. Manifold blanket too. Any heat loss will cause the turbo to light slower.

 

EGT can be easily lowered using an 'ancient' technique called Water injection.
Water or water-methanol mix up to 50% can be used in the intake manifold.
A molecule of water vaporized by high temp increases
it's volume by 1800% while lowering the temp around it.
A molecule of methanol burns generating more power than just diesel.
A 2-3% ratio (water/diesel mix gets excellent results).
It should be limited to hill climbing when temperature start climbing too.
Banks in CA did a lot of research and is recognized in the industry.
Disclaimer: I do not extract any benefit recommending this solution.
I'm not affiliated with any company that sell any water injection devices.
I saw it applied with good results. The engine has to be in perfect running condition, though.
Banks Straight-Shot® Water Methanol Injection