Am, at, catch

These three words, usually in the TRAP set, seem for me to be in the DRESS set, usually.
am [Em]
at [E?]
catch [kEtS] or [katS]
Maybe for the first two it has to do with their being usually unstressed. Do any other varieties have this?

For me, "am" and "at" have [{] when they're stressed, but when they're unstressed they tend to have [E].

And I always pronounce "catch" as [k_hEtS].

Not for "at" and "catch" but for unstressed "am" I'll use /em/ (i.e. the DRESS vowel).

Weird. I didn't think that there were that many variations. [k_hEtS] seems to be the most common pronunciation in the Northwest; most people that I've met from the Southwest seem to prefer [k_h{tS]. However I think it may be idiolectal. "Am" is always [Em]. [{m] is a spelling pronunciation. "At" is most certainly [{?].

I common hear (and myself often use) [E~:m] for "am", even though "at" here is normaly [E{?].

catch [kEtS] is Northern Cities SHift pronunciation, isn't it?
[katS] is advanced CA shift (CA: 1. Canada; 2. California)

>>catch [kEtS] is Northern Cities SHift pronunciation, isn't it? <<

While this may be easily found in dialects with the NCVS, it is not properly an NCVS feature, and can be readily found outside NCVS-influenced dialects. For instance, the NCVS-influenced version of "catch" for me is ["k_hE{tS], analogous to General American /"k{tS/, but I also use ["k_hEtS] as well, practically identifical to /"kEtS/ in other dialects.

<<[katS] is advanced CA shift (CA: 1. Canada; 2. California)>>

Yes I am Canadian, but I don't think I have an advanced Canadian shift. I have a slightly rounded /A/ [Q] and somewhat lowered and/or backed /{/ [a_+]. I write it with 'a' in broad transcriptions because I don't think all the details are necessary every time I write it. It's not quite as back as Jamaican, Scottish or Northern English /a/ though.
I'm not sure whether [katS] is really a native usage in my dialect. It certainly doesn't sound wrong, but I've been exposed to it all my life in American and British media, so it may very well be a 'borrowing' from another variety. I'm much more likely to say [kEtS].