"4' or 5' group" at 100 yards or did you mean 4" or 5"?

What brand of ammo are you using?

Let another person try shooting the rifle.

Make sure you have the correct parallax setting on the scope. Try dry-firing the rifle while looking through the scope on the sled.

Lead sleds have been known to be hard on stocks and scopes. I'm wondering if the rifle has an unseen crack in the stock?
You might be putting too much pressure on the forearm of the stock when shooting off the sled. I'm assuming that the barrel is not free floated. Also...you might be putting too much lead weight on the sled, that makes it not slide back some.
I'm also wondering if you picked up a major flinch? If you have...go back to shooting a rimfire or air rifle --- and work that flinch out.

.Make sure you follow through on the trigger press.

I've never shot off of a lead sled. Try shooting another hi-power rifle on the same rest, or shooting off a 12 pound pedestal rest and rear bag with the problem rifle.

Good luck...

Erno