Slow internet on new 2018 Macbook Pro but not on other devices

[Macbookco5]

I purchased a 2018 Macbook Pro and it has much slower internet speeds than my friend's 2017 Macbook Pro. I have searched various threads with no luck. On the same network, the 2017 has average download speeds of 65 Mbps, 5.85 Mbps upload. The 2018 has download speeds that average 40 Mbps, 5.80 Mbps upload. My iPhone 8 has average download speeds of 70 Mbps, 5.89 Mbps upload. It seems that the upload speed doesn't vary between devices, so what could be happening with the sluggish download speeds on my 2018 Macbook Pro? What information do I need to provide you all for advice? Both Macbook Pros are using Mojave.

2017 Macbook Pro:
Channel 149 (5 GHz, 80 MHz)
RSSI -56 dBm
Noise -89 dBm
Tx Rate 527 Mbps
PHY Mode 802.11ac
MCS Index 6

2018 Macbook Pro:
Channel 149 (5 GHz, 80 MHz)
RSSI -54 dBm
Noise -92 dBm
Tx Rate 351 Mbps
PHY Mode 802.11ac
MCS Index 4

 

[Banglazed]

Try the diagnostic https://support.apple.com/en-us/HT202663

 

[Howard2k]

Do you have the non-touchbar MacBook Pro?
(351/2)*3=527

 

[LogicalApex]

How are you testing speeds? Wireless is a messy beast, but even more complicated is how you're testing the connection.

The best way to get a solid idea of wireless performance variation would be to use iperf to test the connection speed between your wired desktop and both computers individually. This will get you clear performance numbers. Also be sure to minimize any other wireless devices being on at the same time. Keep in mind that WiFi only allows one device to be communicating at a time and all other devices have to wait. This reduces throughput. This is also why I don't recommend testing between wireless devices.

https://en.wikipedia.org/wiki/Iperf

 

[yukari]

It also depends on what website you are using for the test. If you use Google's own, it shows extremely slow speed. However, if you use Speedtest by Ookla, it's completely the opposite.
Here are my results from the two sites:

Google: Upload 1.8 Mbps Download 11.7 Mbps
Ookla: Upload 150.7 Mbps Download 23.9 Mbps

Frankly, I wouldn't trust either one of them.