the full flush is what'* best for your tranny - having them replace fluid while the engine is running. it makes sure that you get all of the old fluid out.
there'* a lot of people who say not to have a full flush done, but i disagree with them. they say that you're going to dislodge a lot of sludge and whatnot that you wouldn't otherwise.
my experience of course, lends just the opposite...
with the new way that they do fluid, it'* a completely seamless event to the transmission. nothing out of the ordinary, as far as it'* concerned. it pumps fluid to the cooler, and new fluid comes back. nothing harmful at all.
when they drop the tranny, there'* actually more of a chance of the gunk falling down, since it'* no longer supported by fluid. i still think that it'* a bunk explination though, as the fluid level is below *all* components in your tranny, save the filter.
so long story short, my informed opinion is...
a) the full flush with engine running is the best thing you can do for your car
b) the full flush won't hurt your car
c) unless you've had serious tranny damage, there'* really no good reason to change your filter. and if there is serious tranny damage, you're going to be pulling the pan to fix it anyway. the metal shavings that are in it right now (that'* supposed to happen, don't worry) aren't of enough size to constitute a problem for your tranny'* lube system. your pump can pull a lot more pressure than it needs to be able to.
96 LeSabre (L36)
95 Olds LSS (L67)