All the training in the world with low power doesn't set you up for departing sea level and landing at Mile high! (MY opinion here).
In our type of flying we are feeling the plane, looking outside, and making judgement calls faster than any computer built. Our minds are alert and sending information to our hands and feet as we make an approach... much coming from our eyes.
Admittedly, I fly low altitude most of the time. Us guys in Southeast Alaska have a hard time heading into the Brooks Range and other places where the 'low' strips are at 3,000' msl; we are used to our base being at sea level- and our DA below. Our eyes tell us we are just off the ground, so the plane will do x... but in reality we might be up at 5,000 msl and it takes a bunch more real estate to turn, climb, approach and land.
When I would head north to fly my friends in for sheep camp, it would take me about 15 landings to get my eyes calibrated for working base camp at 3,000 msl. I had over 6,000 hours total time, almost 1,000 hours in that plane, but would require a couple of days flying before I was willing to set down on some of the 500' strips for the sheep guys.
The speed at which the ground is going under the plane on approach is faster- this messes with your mind, you will want to slow it down- then you feel a stall. For the first few landings you will need to be eyes on the airspeed until you can ignore the speed difference and go back to the feel only.
Your flare and touchdown also change. Your groundspeed is faster, so your drift will be further. Less control due to lower density so more movement to get same results. You might find yourself dropping in a little harder, as your little power blast will also give less effect. Your overshoots will be magnified due to the faster groundspeed...
Solution? Go to altitude and practice, practice practice! The more you fly high, the easier it is to adjust.
On the other hand, watch these guys come from high altitude try to spot land down here at sea level! They think they are in a stall because they are flying so slow, so drop the nose and overshoot. Also their planes jump so fast into the air it scares them!
Practice!
I have a couple of high spots here if you want to come up.