Hello, James here. This sounds more like a hands-on diagnosis is needed here, but maybe we can narrow it down a bit. First off, make sure the engine oil is not overfilled. Even a quart over will cause a vibration. Secondly, when you drive the vehicle, does the vibration follow engine speed, or vehicle speed? Does it change in fourth gear?
The vibration is a steady hard vibration that makes you think the car will cutoff at any second. It can have the ac/heater on or off and it doesn't matter. The hard shaking still continues unfortunately. There is no heavy load on the vehicle, the speed doesn't matter as it occurs at take off and throughout the whole drive whether you increase or decrease your speed...whether you lightly press the pedal to go or not.