@F4mandolin
You've posed a slightly different question elsewhere today, but for consistency with the above response, I'll answer here.
Your comment elsewhere:
"I wouldn't be surprised that we move back to the UK within 3-5 years but a lot of that has to do with how much of a hit I would take in taxes.....If our taxes would be noticeably higher....then that could kill the move before we get going too far."
If I understand your situation correctly, you will have no earned income. That means all your income for US purposes will be passive. As such, you will only be concerned with UK foreign tax credits for the US. For the UK, all income is treated the same within the general concept of taxation, whether it is from employment, pensions, or investments.
Again, you need to do adequate planning (example: as nun points out, the utilization of ROTH's) prior to any tax reporting. Because of foreign tax credits in both the UK and US, and the benefits of the US/UK tax treaty, it's generally accepted that the aggregate tax bill for a year will be no higher than the maximum amount due to one or the other of the two countries, whichever may be higher for that year. The additional cost will be the fees charged by a professional tax adviser if you elect to go that route. I assure you, they will be higher than what you are now paying in the US.
There will be instances, primarily on the US return, where you will not be able to offset tax paid in the UK (such as VAT at 20%, very high fuel duty, etc.). There will also be items that are tax free in the UK, but which will be taxable in the US (ISA's, [winter fuel] benefits, the sale of your home if above the US thresholds, some capital gains if below roughly $15,000, etc.). The UK government encourages people to save by offering tax free financial options. They are NOT tax free on a US return.
Lastly, and I don't mean to be harsh, but if you are serious about this you must do the research yourself for the basic understanding, and you must discover what best applies to your situation. No one can answer for your specific situation on a public forum. (Nun, and others, can offer very worthwhile advice as to what to look out for.) If you feel unable to do that, then start seeking professional tax/financial advice (preferably a tax adviser, not a financial adviser) now.
As always, all the above is only IMHO.