incorrect valve lash adjustment symptoms

[68firebird]

I have a small block chevy, It ran fine on saturday after I put the motor back together from putting new head gaskets on. I figured I'd adjust the valve lash since I pulled the rockers to replace the valve seals. tonight I tried doing the adjustments, and now it runs like dog ****, studders and shakes like a *******. would this be because I have the valves hung open? I've never tried to do the adjustment, and I heard it was easy, but I'm not thinking it was.