From which version to which version are you upgrading? If you upgrade from an older DNN version, are you using the DNN Platform Suggested Upgrade Path -- DNN Docs (dnncommunity.org)?

Did you make sure to meet all the system requirements (SQL Server, .Net Framework...) for the version you're upgrading to?

Happy DNNing!
Michael

Is it just DNN or do you have other extensions as well? I'm asking as I experienced long loading times on an install using a lot of (nested) tokens and I was not sure whether that was DNN related or DNN Sharp related.

I'm going from DNN 9.3.2 (24) on 4.6 to DNN 9.10.2 (0) on 4.8. I have had help from my host provider in doing this. We went to 9.4.4 in the middle there instead of a straight shot. I'm pretty sure we did the Telerik removal, as they were requiring these upgrades for security reasons. It's not my "live" instance yet. They have it on a different server which I log into using RDP and just check the portals on the browser on that local machine. They set up host headers to allow me to use the domains to resolve to this instance just so I can check it before we make it live. I asked if that might be what's causing slowness, but they think it's modules or something else and say they don't provide that kind of expertise and I should ask "a developer." (BTW, I've been working in DNN since version 4 but never on the server side, just the front end.)

I'm not using any DNN Sharp modules anymore, but I did have a lot of third party modules. I spent a lot of time cleaning out what we weren't using. I found many errors in the 9.4.4 interim and cleaned things up. I did it because of the errors, but it didn't start being slow until just at the end of this cleanup.

Honestly, part of the upgrade process should be to remove all unused extensions and upgrade all others every time you upgrade.  This is one of the most common issues I see in some sites that cause issues.  

Once that's done, maybe revisit your performance settings and even make sure you have a WAF (website application firewall, like CloudFlare) to help with performance.  However, DNN should be performing quite well without it.  The main benefit besides the CDN features is the additional protection for your website.  

Next, I'd suggest comparing your web.config to a clean web.config of the same DNN version.  This can help you find other missing updates from previous upgrades and sometimes fixes many issues.  

Here's a presentation that illustrates our upgrade process from last year's DNN Summit conference.  

https://www.slideshare.ne...upgrades-made-simple

Here's a link to this year's conference too.  The early bird rate is almost over.  

https://www.dnnsummit.org/

Typically if you are seeing slowness after doing a cleanup of that nature I would start looking at the logs to see if there are recurring errors that are happening that you are not noticing.

Check the /portals/_default/logs directory
Check the Exceptions, ExceptionEvents, and EventLog tables in the DB, are they huge?
ANother common problem on older vintages is a large ScheduleHistory table.

This is in addition to the other recommendations