2017 was a good year for mobile users in the United States - Verizon launched its unlimited data plan, T-Mobile responded by one-upping its costs, AT&T followed two weeks later, and Sprint went one step further with prompting users to switch from Big Red. But the Unlimited 4G revolution came at a price - speeds went south. The situation improved in the three-month period, ending in November 2017, where all four major carriers saw LTE speeds improve, even if AT&T and Verizon are still struggling to reach their initial speeds. August saw all-time low 4G speeds for AT&T and Verizon...
Source: https://www.gsmarena.com/4g_speeds_us_improve_after_launch_of_unlimited_plans-news-29222.php