This has been discussed at length in other threads, so I will summarize....for some reason, in last two seasons, plus the "Last Salute" episode you mentioned, the character of Columbo was changed from
what I call "modest and mildly eccentric" to "arrogant and goofy". This "arrogant and goofy" persona is quite noticable in "Last Salute", "Murder under Glass" and "Make Me a Perfect Murder", however there are episodes in the last two seasons that have in his original, better mode, such as "Fade into Murder" and "The Conspirators". I don't know who is to blame for this, the producers or Peter Falk, but I must admit that Peter Falk's status as an actor is somewhat degraded in my eyes (as good as he is) by his allowing the character to change in this negative way. I compare him unfavorably to another favorite of mine...James Garner in "The Rockford Files". He had to work a lot harder than Peter Falk (he made far more episodes of a weekly series) and he NEVER put in a bad performance.
In any event, in the episodes of the 1980's revival, he ONLY plays the "arrogant and goofy" role, and so as far as I am concerned, they are not "Real" Columbo episodes, although there are other members of this group who disagree with me.

I used to think the last 2 seasons must have been filmed much later as Peter Falk seems so much different. I find his mannerisms different and also his voice which seems rather muffled. Does anyone know why he changed ?