When you ride in the mountains, the air is thinner so the engine will run too rich without a correction to the computer’s fuel map.
Ducati’s engine management system takes input from an atmospheric pressure sensor that monitors the atmospheric pressure so that the computer will supply additional fuel at lower elevations and up to 8% less fuel at altitude.
Unfortunately, 8% is often not enough so the bikes still run rich at altitude. Earlier model (851) base fuel map corrections went as high as 32%. Unfortunately, they really ran crappy when the sensor failed so Ducati changed the programming to max out at 8%.
The sensor's output varies for pressures between 17 mm Hg (0.25 volts) and 787 mm Hg (4.75 volts.) So an open circuit (0 volts, a common connector failure) makes the computer think that the engine is operating at a very high altitude so it reduces fuel by the maximum amount to compensate.
It used to be that you’d get around a 13% correction at 1700m but now you only get around 5% with the stock chips.
So, the solution to your problem is to get an EPROM that uses a larger (32% max) fuel map correction for altitude.
The UltiMap chips can be supplied with the altitude correction recalibrated.
http://www.fuelinmoto.com.au/ They state: “Simply add a 'P' to the order code (for example UM081P). These need to be ordered specially, as they will make your bike run poorly if the altitude sensor develops a fault.”