I have a 2019 Chevy Silverado 1500 6.2L Ltz and had unlimited data plan through wireless carrier AT&T and got around the same speeds as the original poster, 2.5-3 Mbps. Did the reset and everything through OnStar and no improvement. Phone hotspot is obvious way to go at that point. $20 a month for unlimited seemed very fair if data speeds were similar to cellular speeds considering we are getting 80-120 Mbps through cellular