Hi Gary.
Welcome to the forum.
What are your results with a very simple test form? One or two views.
I would look at ways to consolidate your views such as using conditional formating to just hide certain sections on similar views.
I am guessing your schema is also fairly complex.
From an architecture standpoint, to move this to a better performing design, typically I would do this:
Use a backend database with web services to house your source data and collect the user's input.
Identify each user as they open the form, this can be done with an Active Directory web service.
With these two steps you can then allow the user to use multiple, smaller forms and the data is shared between them since we know who's info it is.
With this, you end up with a more typical client server application which can perform well while manipulating and collecting your information.
For most functionality you should not need any code or anything elaborate other than this design change.
You can also attach a zip of your form and XML files in a zip and then I could try it out and see how it performs for me.