Tony is right. Night temps are the criytical issue with highlanders. We have some highland plants here in our 12 feet above sealevel greenhouse in south Florida. Winter temps are fine for most, but its the summer that's killer. Our summer nights can consistently run 78-80 degrees F for months. We've pretty much established that if a Nep comes from about 700 meter altitude to about 1100 meter altitude, it will survive but definitely slow down and stop pitchering for 4 to five months out of the year. Neps that typically grow above 1000 meters really suffer or flat out die. Clyde Bramblett kept N. burbidgeae going in his big greenhouse for years before Andrew decided to relocate it and several hundred other Nepenthes somewhere out in the everglades. During the summer, it would stop pitchering and stall its growth, but pick up again in fall when night temps would drop.
During winter, day temps in our greenhouse may reach 90 degrees F, if for only a few hours, but nights would be between 55 and 65 F, with the occasional cold front night plunge down to 50, when heaters go to work. What is interesting is we have noted a sort of temperature "sweet spot", where lowland and many highland Neps can grow side by side. With lows of 58 to 65 degrees F and days topping out at 90F, you can grow highland veitchii, maxima, burbidgeae and other lower montane species side by side with bicalcarata, sumatrana and northiana(as long as constant high humidity is maintained).
Hope this is helpful.