I need help figure out the problem with my car and have no Idea what it is or what to do

Its a 93 olds cutlass ciera, it is missing and it like runs ruff at times and sometimes its ok but its worse when ur driving down the road and when u are stopped like at a light it sounds like its going to shut off like if the battory is weak and we took it to auto zone and they did a battory altanator test they said it was ok the battory lost 2 volts and they the ones that said that it was missing and there is no engin light on and we took it for a dianstic they run it for like 5 min if that and came up every thing ok they also tested the wires and they said they are good but it still doing that some say needs plugs but I need to know what it is forshure cuz I dont have the money to fix things on the car and its not the problem. And we did have to put a new fuel pump on and filter about a month ago. And before that we did an rator flush. Also I did notis when u are driving down the road like 40 mpg and when u need to push the breaks to stop at a light the car shakes a little never done that before it started that after we had that pump and filter put on then it was notis like with in 4 hours after I left the shop like u can feal it shake and see the hood shake.