1988 Buick Skylark RPM's Drop and car Shakes

If the RPM's drop and you feel a vibration, chances are the problem is the engine is missing. I would start by checking fuel pump pressure.

Here is a how to:

https://www.2carpros.com/how_to/how_to_check_fuel_pressure.htm

Something tells me you are not getting enough fuel. If the pressure is low, check it before the fuel filter to make sure it isn't plugged.

Let me know what you find. Also, I am assuming that the check engine light hasn't come on because you didn't mention it.

ALso, most parts stores will lend or rent the pressure gauge you need.

Joe