change trunk group x", remove all members referencing the card.
"remove sig x", remove the signally channel (if it was a PRI, unlikely on a G3siV5, since PRI only came out in V6 I beleive)
That should do it, then you can of course do a "remove ds1 01AXX", and totally remove it, once it is not being referenced on any signalling or trunk group form.
You might also have to do a "change synch", and pick a different synchronization source, if that DS1 was being used for that (temporarily, you can put it back later)
Mitch
AVAYA Certified Specialist