Yesterday on my way home the car in general started shaking under load and today when I started it, it was still shaking at idol. 96 z28 lt1 240k miles on engine

 

How long since the spark plugs, wires, distributor, and O2 sensors were changed? Is the SES light on? Have you checked for a broken engine or transmissions mount?

 

The water pump, plugs and wires were replaced last month. The service engine light is on, but it has been running fine until now. I don't think anything like the motor mounts has been replaced on the car.

 

with the barking brake set and tire blocked forward with engine running and trans in drive....give it some throttle...does the DS engine lift more than a 1"

if so your motor mounts are done

misfire/shake under load can often be plug arc or bad plug wire. A fine spray mist of water on spark plugs and opti plug wire boots can reveal "arc"

If CEL is on pull the code.

 

Had same problem today tightened up the intake around the maf, it was leaking and causing the engine to act up all over the place and would not work under load. Could be a possibility, was for me.