If you have followed the documentation this means that you have done only changes that are persisted to the database i.e configuration changes to the Plugins like creating a Slider etc.
So all the changes you have done will be automatically available in 4.4.
If you have done modifications to the theme files i.e .cshtml files then you would need to make these changes again in 4.4.
We will need a little bit of context here.
Are your tests hitting a single page where there are some Sliders?
How many Sliders do you have on that page and with how many images?
Do you use Conditions or not?
If you could get your clients login credentials and submit a ticket on his behalf will speed up the whole process of investigation (let's start with this optimization first :)))
We support all the databases that nopCommerce supports.
Only the Ajax Filters plugin does not support PostgreSQL but it supports MSSQL and MySQL.
Please note that we offer 1 year of free support as part of your product purchase and we can't afford to provide free support forever (no company in the world can).
I understand your frustration since your license has expired but we can't investigate the issue you are having without access to your store and it is not OK to share access to your store here in the forums. That is why we requested you to submit a ticket.
If you can demonstrate the issue without the need to submit a ticket please feel free to do so and we will advise.