Same thing happened to me last year. My GTA V(steam) was working with little to no issues, until the Diamond Casino update. After that update, as you've mentioned, my game would stutter a lot 10 minutes into the game. I tried googling this but couldn't find anything helpful.
Seems like Rockstar is just disregarding old systems as they're moving forward with the updates. I wasn't able to play till I changed my processor. [ Core 2 quad Q6600 to Ryzen 3 3200G, the CPU was so old that I had to upgrade almost my entire rig]