1998 Lexus GS 300 car problems

1998 Lexus GS 300 Automatic 2000 miles

hello my lexus is shaking real bad when it sits for hours then I go to crank it it shakes or about ten min like a rollercoaster then when time to drive it it s=cuts o and then I i go 50to 60 miles and hour it makes a knocking ound like thump thump real loud and the speed drops and I have to put my feet all the way down to the gas pedal to pick up speed. I have been told and bought so many things and it is still doing the same thing fuel ilter was put on, sparkplugs, throttle position sensor now I was tod the cadallac converter and the timing is off. I really dont know please can u answer this question so people can stop guessing thank u