1995 Chevy Camaro Bad Chatter

I just replaced the head gaskets on my sons 3.4L Camaro. All went well and it started and seemed to be ok. We took it for a ride and it is lacking power. I drove it further yesterday and I floored it and it stumbled pretty bad then I let off the gas and it picked back up. I got back in the car after that and now it sounds like the valves are chattering very bad. Running even worse. All I can think of is the valve adjustment. I adjusted them like the manual said. Tighten untill the play is out of the push rod then another 3/4 turn down. I made sure the push rods were in the lifters before the adjustment. My only other concern is, I had my son jack up the car (hes 15) and I did not catch it but he was jacking it on the oil pan. So my concern is that maybe it closed the gap to much between the pick up tube and pan and maybe it was not getting enough oil to the Hyd lifters. It does not appear its caved in to much. Any ideas before I take the upper intake and Valve covers off again. Thanks for your help in advance. Neil