Convincing my DBA there's a sporadic issue with the SQL Server
Start with Tara Kizer's post on Getting Help with a Slow SQL Server. (Disclaimer: it's on my company's blog.)

She walks you through:


Getting your server's wait stats since startup with sp_BlitzFirst @SinceStartup = 1
Getting server health data in Markdown format so you can copy/paste it into your Stack question with sp_Blitz @OutputType = 'markdown', @CheckServerInfo = 1