OK, so I pulled the third member out this weekend and it appears that the axles are not 31 spline like i was told and seem to be 28 spline. Visually, they looked like 31's but i have counted the grooves about 10 times and still come up with....28.

I realize the 31's are preferred but is there any issue with keeping these in there for a trail rig?

If I replaced them, what else in the rear would i need to replace? Trying to do a cost/benefit here....

Depends on how much you like changing axles and how hard core your wheeling is. 28 splines is fine for light duty wheeling, but if you're going big tires, locker, and harder core stuff 31 splines are a good investment. The main thing you'll need to change to make the upgrade is your diff. You can use the same carrier and gears and most of the other major stuff is the same.

You can buy upgraded/aftermarket 28 spline axles that will be better than stock without changing the diff. Probably strong enough for most EBs.

How can you tell if these are aftermarket or stock 28 spline. He was running 4:56 gears and 35 inch tires.

Hard to tell unless there are manufacturers markings on them. Stock 28 spline can handle quite a bit of abuse.