Rocker Arm ?
The pushrod is not seated properly in the lifter. Take the rocker arm back off and properly reseat (center) the pushrod back in the lifter. Then re-install the rocker arm.
Might also check the pushrod for straightness by rolling it on a sheet of glass prior to reinstalling it. You may have bent it while tightening it down when it was not seated in the lifter properly the first time.
Ron,
And I'd be *REALLY* impressed if you somehow managed to mis-seat the pushrod on the lifter....the plastic ls1 guide cups make it really really really hard to screw up.

