Emails taking a long time to display messages in the Preview window
I've been having issues with my email taking along time to display the message in the preview window. iMac is a late 2015 model, 3.2 GHz Quad-Core Intel Core i5, 32 GB memory, using Monterey 12.6.3 and Mail 16.0.
After new emails download, I click on one of the new emails and nothing displays in the preview except I can see who the email is from, the subject of the email and "To" and "Reply-To" lines. I'm using the "Side Preview" option in mail.
One after the other is like this. I can hide email, launch Safari and surf the web for a few minutes, come back to mail and then finally the messages will display. Sometimes there is no delay is the messages being visible in the preview window. Even have issues with emails I've already looked at but kept in the inbox taking minutes to display again in the preview window. I've tried rebuilding the mailbox which seems to help temporarily but then it acts up again.
I'm wondering if I should try deleting the mail preference file? If so, where is this file located? I've looked but not sure what file I should try deleting or where it is located. Anything else I should try.
This is so annoying, to say the least, especially when there are 40-50 emails after I get home from work.
Thanks in advance for your help/suggestions.
iMac 27″, macOS 12.6