Unstable Ping - PS5 - Unplayable

Each evening, I log on hoping to be able to play, but no matter which server I select I'm unable to go longer than 10 seconds without the game lagging. Even in town with me not moving. I pause and go to Options to see the performance graphs, and my ping goes from around 100 ms and fairly stable, then spikes to 3000+ for a second or two, then back down.

I have used an app to monitor ping on my modem and it stays stable at around 90 ms. My highest spike was 230 ms. No other application has performance issues at all, and my PS5 states a connection speed of around 180 mB/sec. Internet is T-Mobile Home Internet, which has stayed stable the entire time I've had it. New modem within the last month.

Even just standing in town at the stash, I can navigate through the stash with no hitches while the town animations in the background (such as on Ardura Caravan, the rhoa guards and the wheels, etc) will freeze, then fast-forward to catch up.

I'd be playing every night if performance would allow, but currently the game is unplayable for me. Randomly, I'll have one night out of each week or so that will operate normally/smoothly, but that's the best I've gotten.