When you leaned your engine up you created more power. This in turn would have increased your rotor headspeed making the Heli much more crisp. The usual 1/2 stick hover that you probably had turned into a rather abrupt lift. All your controls would have responded much smoother and quicker with the raised head speed! Could not have been that loose. Sounds like you were learning at your own pace quite fine. There is a lot of older Shuttles out there still teaching people to fly.
I will have a rather biased opinion I love Shuttles. A lot of the parts you have will interchange with the newer kits maybe. Do you own an original Shuttle with the blue canopy or white canopy or do you have A Z or ZX ? The one new for 159 is that the Z-TS or the shuttle plus?