Need some advice on T-Mob Gateway

I just switched from Verizon to Tmobile cellular internet. Overall, T-Mobile is killing it. Here's what I don't get. I don't see any way to configure the Gateway how I want it. Shouldn't be a big deal, I can throw my ASUS ZenWiFi Pro ET12 AXE11000 behind it right? Well yes but it's like t-mob is throttling that connection. When connected to t-mob wifi, over 600 Mbps dloads. When on Asus wifi behind it, under 300, usually around 270-280. That's a massive difference. Asus is fully updated and running optimally. I'm wondering if it's signal interference from the t-mob gateway? I don't want to use their gateway but I also don't want to drop half my connection speed. Any thoughts or ideas on this? I wish I could get into the t-mob gateway and set it to pass through, turn off all wifi, and see how that acts but I'm not seeing any admin access. Open to any info, suggestions, thoughts, etc. Thx!