Most shows peak in their first (https://screenrant.com/tv-shows-peaked-in-first-season-1-one/) or second seasons. What are some examples of series that peaked later (https://www.theatlantic.com/entertainment/archive/2014/07/why-most-tv-shows-peak-by-their-third-season/374750/) on in their runs, and when did they peak?

Everybody Loves Raymond peaked between the 4th and 7th seasons.

King of Queens.

Its first seasons weren't that strong, and it peaked later, and is appreciated more even after its network run.

During the 2000's, Will & Grace was far more regarded.

While King of Queens wasn't on the level of Seinfeld or Friends, it was far better than Will & Grace, but didn't get much recognition then. It has outlasted Will & Grace in syndication and airing.

I definitely agree with King of Queens, as Favoriteshow says. The show got better as it aged. It was always good, but it became hilarious. I didn't start watching until summer 2005.

I kind of disagree with the assertion that most series peak in their first or second seasons. For bands/singers with their first or second albums, I concur, but with sitcoms it may take a few years for the writers and the acting ensemble to really know their characters and for the actors to know how best to interact with the rest of the cast.

Yep - I also disagree with the original assertion. Most successful series don’t creatively peak in their first or second years. There some exceptions of course.

Everybody Loves Raymond
Roseanne
That 70's Show

Cheers began to get its groove around season three.

Friends
Seinfeld

It's a Living really improved when Crystal Bernard was added to the cast for the syndicated version. Then it peaked when Sheryl Lee Ralph replaced mediocre Ann Jillian in seasons 4-6. Star Trek: the Next Generation peaked starting in season 3. Star Trek: Voyager was at its best for seasons 4-7. Seven of Nine replacing Kes was a substantial improvement. Law and Order was a really dull show when George Dzundza then Paul Sorvino was the law star. Jerry Orbach started to put Law and Order on the map, then overall cast was made stronger starting in season 4. Benson was already a good show from the start, but Rene Auberjonois replacing Lewis J. Stadlen in season 2 made it fantastic during seasons 2-5. Wings was already an excellent show, but adding Tony Shalhoub to the cast in season 3 made it even better. It is too bad though that NBC forced Wings to cut its gorgeous theme song then.

If you want examples of shows that peaked after the point of becoming eligible for off-network syndicated reruns, look no further than NCIS (seasons 6-13) and The Big Bang Theory (seasons 6-8). :)