Help with gaggia classic temperature

I’ll try to keep this short, I have watch countless hours of videos from Lance on espresso, I’ve focused on everything possible.
I have the newest gaggia classic pro and a gevi velpro grinder.
I have just the most inconsistent shots even though I’m focusing on every variable and my conclusion is the temperature coming out of the group head, my shots are typically on the sour side but every once in awhile I hit a stellar shot.
It’s a brand new machine, preheated for like 30 minutes prior, I checked the water temp coming out of the group head and it’s around 175-185, I know I need to get a gaggiamate etc but I just spent so much on all of this stuff and am not ready just yet.
I tried using the steam button to temp surf but it’s all so unpredictable and frustrating