JAJ

Definitely get some professional advice but at the same time be an informed client. When you do that, you should discuss - in relation to your pension funds - that in the USA, as a general rule (there may be exceptions), it's usually not "income" until you legally have access to it. If it is income, then consider tax treaty provisions. Usually the deal on income is that you pay USA tax but can claim a foreign tax credit up to the USA federal tax rate. If you pay State tax it's additional, no foreign tax credit usually available.

If you have large capital gains you may want to crystallise these before you take up USA residence, although you also have to consider the position in the UK and Switzerland.