Sounds like Predator cap curse. As a hemi, both the intake and exhaust valves each have a lash cap sitting on top of the valve stems. Just a little pea-size cup sitting mouth down on the valve keepers, so that the rocker arm is pushing down on the cap and not on the valve stem. (Except non-hemi, I think they only have a lash cap on one of the valves.)
The cap curse is you unknowingly letting a cap (or both) get pushed off, maybe with your feeler gauge, leaving a huge amount of flapping around by the rocker arm, letting the pushrod fall out from under the rocker. The caps usually fall down the pushrod openings into the case, where they seriously need to be removed before running it again.
Trying to adjust the lash without the caps won't work, the excessive tilting of the rockers will prevent the valves from operating in correct lift and duration of the cam.
Pull off the rockers enough to see if both valves have a cap sitting on their stems, or if you've adjusted the lash with the rockers pressing directly on the stems. If missing, look for them in the head space there. If gone, you've got to split the case and get them out of there.
Please don't split the case without a new sump sidecover gasket in hand. People who live by gasket sealer have troubles with shaft spacing after putting it back together. If you're ordering a new (for hemi only) gasket set, might as well get a hi-performance set with a thin racing head gasket for the same money. Mine was $14, came with a .012" stainless steel head gasket. Noticeably increases the performance due to the increased compression.