You need to spin the nuts on all the way down to the rod cap, if they do not spin down all the way easily, the nut or rod bolt should be replaced.
If you need to replace your rod bolts, normally you need to recondition/resize the rods.
Stock GM rod bolts are not much money I believe they are also not that strong either, so I would recondition the rods & use new rod bolts & nuts.
MBHD
