T-Mobile Home Internet Slow IPv4

djb14336,

I'm not exactly sure what you mean by "let everything ultimately use their DNS as primary" but I think you mean don't use any third-party DNS provider. I'm not sure why this would affect latency other than a NS lookup. In my case, Bing.com, which was already resolved has a high latency
I don't understand the rest of the paragraph. 

"Queries to an external v4 DNS will have to go through their funky 464xlat/CGN tunnel crud to get there and back"

Again, bing.com was already resolved to an IP address. 

"you can change the private address space if you want, so if you are doing a double-nat set up (personal router in NAT mode not as an access point), you can set them up with more unique IP ranges."

I'm not sure what that has to do with anything, there's double-nat many places and the latency is sub 5 ms. 

" The Askey forwards it over it's v4 private LAN subnet, and if you are using your own router in native mode, that will have to forward again to it's private LAN subnet.  This will inject a little extra lag, but should be considerably less than what you are getting trying to force google/cloudflare/others as the primary DNS.  For the clients you configure manually, would want to point to the router(s) first, then any external provider you want to hit.  Por ejemplo:
10.10.x.x (personal router in NAT mode), 192.168.x.x (TMO Askey)
(Put the local gateway with better response time first, then you can list external providers as you see fit), 8.8.8.8. , 1.1.1.1 "

Not sure what you mean by all that, and again, the double-nat does not account for that IPv4 latency it that translation is sub 5 ms, it is negligible. 

" Forget where I got referred to it, may have been speedguide.net.  But there is a DNS Benchmark tool you can download for free that you can use to test responsiveness of your DNS setup.  May want to Google for it, just make sure it is coming coming from reputable source and all.
EDIT:  found it…
https://www.grc.com/dns/benchmark.htm
Hoping they start shipping the new 5g hardware soon so we can get a feel for how they hold up.  The bands have been available in our market for quite a while now... but we are all still on the Askey LTE boxes. "

Again, it's continuous data latency, even after a DNS server resolves the name to IP address. It is the entire IPv4 experience from a simple ping to bing.com to loading a simple website. Even worse than the latency is the dropping of packets. It gets so bad, TCP does not account for it. It becomes an unreliable connection worse than dial-up. 

Jason