The easy part. Should I fill my tranny with ATF+4 or search for +3? It seems
most of the local places only have +4 now. It's a '93 Grand Voyager 3.0L, 3
speed auto (A670 I would imagine), 203k kms.

The harder part. This tranny has always had hard upshifts, especially when
cold. By hard I mean it bangs into gear with a good jolt even when very
gentle on the gas. The first 1-2 and 2-3 upshift is usually very hard, and
it usually shifts hard when between gears in stop and go traffic. It's
usually a little less violent (sometimes downright smooth) if I stay on the
gas a little, which is tough in traffic. Not a new problem, it has been
doing this for years now. The previous owner (my late father) never
considered it to be a problem but obviously something isn't right. It never
EVER slips, it just bangs into gear. What are the odds that a simple band
adjustment would help? Anything else I could check? Symptoms seem odd too me
for a bad mount, what do you guys think?

Now that I think about it, would running Dexron cause the rough shifts? I
did a pan-change a while back with ATF+3 and it got a little better for a
while, but that was by no means a complete change. If it had been filled
with with the wrong fluid at some point before that... Whatcha think?