A little update:
I disappeared from this thread due to the massive shock of a possible huuuuge tax. Once I realised that the threat was very real my focus shifted from the practical sides of moving, and I have been in tax crisis mode the last days. I have spent my time researching IRS's webpages, talking to my parents and in-laws and even a tax consultant specializing in international tax.
I found that you were absolutely right about the currency transaction gain tax, and that I might have to pay around $20 000 to the IRS if I sell my apartment after Christmas!!! My husband might have done his taxes the wrong way earlier by not reporting my Norwegian income, and this situation is equally bad for him, not just me. But thanks to this forum we found out in time, and have now taken several (legal) measures to avoid this tax. I will not be going to Texas this Christmas (which sucks so much!!), and I will sell my apartment to my parents before the end of the year. That way I will pay back the mortgage before I become a US resident for tax purposes. We still haven't talked to the bank, but we've looked into ways of doing it. My husband and I will proabbly sign a prenuptial agreement (should have done that before we even married!), and he will have a statement on his 2015 tax return saying that he is filing his taxes unaware of any international income his wife might have (which is true - he really is clueless about my finances).
Summed up: You might have saved me a bill of $20 000! THANK YOU!
And since I'm on this tax rant and have been going through my Norwegian taxes: I paid 26,8 % tax in 2014 (on an income of 518 000 NOK), but expect to pay less this year due to the tax benefits from having a mortgage in Norway (there are some upsides).
And lastly: Norwegian food is not gross :) I have some favorites that I will take with me for sure: crisp breads (I make my own), sour cream porrige, Norwegian pancakes, fish burgers, school buns and meat cakes. Others will be missed dearly: Macrell in tomato sauce (in a tube), fish balls in curry sauce, salt-dried lamb, lamb-and-cabbage.. :)