335xi lack of power over 4000 rpm and 80mph, somebody else?

Hi everybody, three months ago I bought a brand new montego blue 335 XI. I live over 12,000 feet and I have noticed that over 80 mph and 4000 rpm the engine seems to loose power. The best way to describe what happens is to imagine that the engine after 4000 rpm begins to cough. Therefore, I have to change gear lets say from 4th to 5th, and then everything goes well, until you reaches 4000 rpm again.
Is it related to the turbos?, it is like the engine cannot breath well.
Is there a way to help the engine breathing better?

thanks!

Dude, anything high performance will lose power about 12,000 feet. That is over 2 miles above sea level! In WW2 the aircraft had superchargers on them to increase the air flow at that altitude.

I really don't know what to tell you other than open up your intake , get a K&N air flow system and lean out your car.

My gut tells me unless you are pushing the turbos (which are exhaust driven) you are dealing with an o2 problem.

Where do you live?

Bill (happy at 582ft)

Thanks Bill!
I***180;m beginning to believe that my problem is due to the high altitude what it is a pitty. Anyway, I am looking for replacing the intake, and perhaps changing the intercooler. Somebody told me that a new intercooler might get denser air to the turbos.
If you have any suggestions, they will be welcome.
Btw, I live in La Paz-Bolivia (South America). The highest capital city in the world