Last summer was ‘T-Mobile - 1 ½ years later’ - this is an add on for the since last summer.
Skip to summary if you don’t want the long version.
Road trips in SoCal/Central Cal, as well as New England (MA/NH/ME) specifically.
In my area of SoCal, many (2/3) of the local sites have been upgraded from either LTE (B2/B66/B12) to 5G (B2/B66/B12/B41/B71 + n41/n71). Most local areas have overlapping coverage, making n41 usable ‘outdoors’ throughout many areas. Sprint sites (some) have been rebuilt, others have been powered down (many either colocated, or very near T-Mobile sites).
Further outside my local area, rural coverage still remains mostly as is, or sites have been upgraded.. but in many places still poor coverage. Ventura County areas have been updated somewhat, I think there were quite a few Sprint sites/users to convert/migrate. Not all are completely upgraded (eg. a former Sprint B26/B41 site now just shows as T-Mobile B41, no 5g or PCS bands).
Up the coast at Gaviota, with 3G being disabled, AWS is a bit weak, and ends up on GSM (GPRS) 1900, or worse … roaming on AT&T. Sites in Solvang area now are 5G/5G UC (last year this area was LTE only), similar when hitting Morro Bay and even San Simeon CA. Performance was a little sketchy between Gaviota (GSM 1900) as it roamed onto AT&T, which became useless, and wouldn’t revert back to T-Mobile until a reboot at Solvang.
Cambria, CA (pop ~5000) is an unusual one, as it has a small site which covers ½ of Main St. on LTE AWS / 3G /2G 1900 only, while ~3 miles north in San Simeon (pop 450) has 5G/5G UC .. but also from a small site. In this area, speeds increase in .. a spot where few are, but coverage is has not.
Going to the East coast, Boston now has quite a bit of n41, where it was mostly LTE and B71 / n71 last summer. Going up I-95, there’s a good bit of 5G, and coverage is decent (note: in ME itself, most coverage is B71/n71 due to the rural nature).
Bangor, ME is an unusual area. n41 exists… but not in much the downtown area. The downtown area actually still runs Sprint B41, which was 2CA 20MHz last summer, but cut back to just 10MHz this summer. T-Mobile says it may be another year or 2 to upgrade sites.
Rural Northeastern Maine is a strange area. Much of this is roaming, which is fine. Lincoln, ME has 5G UC (which is good) - only 40MHz on n41, but still is good, considering how small the town is, +400Mbps. Beyond Lincoln, is where items get strange. Roaming ‘defaults’ to AT&T (eek) at ~256kbps. US Cellular is available … but you would have to manually select it. US Cellular has LTE + 5G roaming of up to 3Mbps (much more usable). I find it ironic that T-Mobile would have AT&T as its primary roamer over US Cellular for this area, given the performance caps., but that’s probably a business decision.
Summary: Many areas now 5G UC now, giving urban/suburban performance a boost. Rural areas are being ‘upgraded’ as well. In the areas that I’ve been to, not many ‘new’ sites for rural or to fill in the coverage gaps. Some areas (eg. Ventura) are still a large work in progress, a few have gotten worse (Gaviota). Claims of ‘most 5G coverage’ really only means something for sales, or for those with poor performance. T-Mobile has made good strides in urban ‘performance’, however, it still has a long ways to go for more rural areas, and those haven’t really seen any improvement since B71 was deployed a couple years ago.