Any UK/US dual retired people out there

Are there any UK/US dual citizens out there who have retired back in to the UK
who have actual experience dealing with UK/US taxation, 401ks, IRAs
UK and US state pensions etc? Your stories and advice would be welcome
as well as any recommendations for companies to help navigate the
issues.

You need dual advice both in the UK (in particular) and in the US.  The rules in both places plus the US/UK treaty make this pretty complex stuff!