The vanes default to wide-open, and with the engine off will rest at that position. On startup they will wind in to their minimim-aperture positions, reducing the effective size of the turbine inlet but keeping the gas flow smooth: minimising the aperture increases the gas speed across the turbine blades to get it to spin up earlier and give boost at lower engine rpm. As soon as the turbo hits max-boost the vanes start to move out under ECU control, increasing the effective size of the hole through which the gas flows and keeping the turbo at max boost while reducing the impedence to the exhaust.
The VNT turbo's are sized so that max power is reached when the vanes are fully open. These turbo's don't have a wastegate.
Having said that, I thought that all the non-diesel turbos (and a lot of the diesel ones) were not VNT - but I'm away from my references at the moment.
Wide open vanes shouldn't cause limp mode, but will reduce boost at all rpm except max, making the car feel vastly underpowered, a lot like limp mode in fact.
Lots of good advice given above, all of which I agree with
If I were you I would change up at higher revs. Your peak torque is at 2200 rpm, and I think that one strategy for good performance is to change up so as to drop back to the torque peak, so changing up at 3-4000 rpm I'd guess. Changing at 2500 will drop you down to 12-1500? which is well below even a VNT turbo's boost threshold, so you're wasting fuel pushing the turbine around without getting enough of a boost from the impeller to balance it. Turbo usually starts to be effective at 1800 rpm, I think (although I have a diesel, and they may be different in turbo range).