Automatic 84 Firebird shifting problems

Jerks how? You said when hitting the gas from a stop.... And you said it jerks from 1-2 shift... Does it jerk taking off AND shifting from first to second? Be a little more specific please but what I'm thinking is a bad transmission mount....you would feel this any time you hit the gas hard, and during hard shifts you would feel a pronounced THUNK. You can test this by putting the car down in 1 (Low) and with your foot on the brake, apply throttle lightly to moderately in spurts to make the car want to lunge a little bit. If it has a transmission mount bad, it will thunk every time you apply the gas.