Shaking really bad and rumbling sounds/ really slow

it rumbles as you are about to stop, well that depends.

if there is a vibration AS you are applying the brakes, and about to reach a stop, it could be that your brake rotors need machining, or "turned"; however, in this case, you would also hear a grinding, as well as feel the grinding through your foot.

there is also a "rumbling" associated with a strut mount gone bad; however, this is more of an audible clanking, and is also audible when driving slow on a bumpy road, and not really specifically in the process of stopping.

for either of these, please stop using your radio, and possibly open the windows, to better describe the sound.

IF the car shakes when sitting at a stoplight, or such, please watch your rpm gauge (tachometer), and see if the idle speed is exceptionally low or erratic.

if this is the case, it may be that your throttle positioning sensor, mass airflow sensor, or the like, is malfunctioning, and is giving a warm engine a fuel/air mix appropriate for a cold engine.

Sounds like it is running on 3 cylinders! Probably a faulty coil pack!

Sounds like two separate problems. The tranny is an issue all on its own. If the engine is running rough and smells like gas, that would indicate its running rich and/or having a misfire on one or more cylinders. I would check with ignition system first, spark plug, wires, coil.

Sounds like a really bad vacuum leak, and or possibly a dead spark plug or wire. Check under the hood for a hissing noise. Broken, loose or missing vacuum line. Change spark plugs and wires.

Sounds like you blew her up bud.

Sounds like a bad wheel bearing to me. Jack up each corner of the car one at a time and grab the tire. Shake like crazy on it - if it moves, you've found a bad bearing. It should be solidly on the hub with no play whatsoever.

I don't know how much oil you had to put in but it sounds like you have maybe more than opne issue and both sound major. One is engine reving and speed not picking up sounds like trans problem. Two the engine shaking and making noise and being run low on oil leans toward possible engine damage. If your mechanicly inclined check all fluids and when checking trans fluid smell it. If it smells burnt the trans has been damaged. Check oil pressure and make sure coolant is full.You may have to take it into the shop.

Do you have the 3800 V6? It sounds like a bad bearing. Most likely the tensioner pulley or alternator.

You have a shot front wheel bearing which will sound like a whining rumbling noise, if the bearing is really bad it will have started to break up inside and the streering wheel can snatch.

Guy with a trolley jack can tell you in a few minutes how bad it is