car shakes back and forth please help

89 toyota tercel auto transmision

ok my car is fine going under 60km/h on flat roads but when i hit the highway and try to go faster than like 135km/h it starts shaking back and forth and slows down i have to let of the gas and try to go like 90km/h it sounds like its clogging and doesnt want gas wich lead me to believe it was the catalitic converter [recently i have ruled that out because i now think its that my cylinders are dirty and need to be cleaned am i right??] also it does this when i have ppl in my car and try to go up a hill, it feels like my car has no horsepower and when i try to get alot out of it the car just shakes back and forth and slows down

this problem has plagued me for years has this ever happend to anyone before am i right in thinking its the cylinder that need cleaning please help. someone told me this was a common problem but it doesnt seem that way

Try giving it a good tuneup. Fuel filter, spark plugs/wires, distributor cap/rotor, pcv valve, air filter.

Ditto the good tune up.

Try giving it a good tuneup. Fuel filter, spark plugs/wires, distributor cap/rotor, pcv valve, air filter.

i have recently done all of that except the pcv valve wich i dont think is the problem nice try though

i also changed the water pump and have gotten my hosses pressure chekd and have recently given her a oil change and changed my headers to exhause pipe gasket the transmision fluid dosent smell like burning and i hate my car

can anyone back me up on thinkin its the cylinders that need cleaning?? or if i do this is it just gonnna go up on the things ive done list wich havent fixd this problem

Never heard of cleaing cylinders, not quiet sure what that means. You could run some fuel system cleaner though it, theres some stuff called Sea Foam that works better than anything else I'v tried, I'd put a can in the gas tank and feed about 1/2 a can into the intake (has instructions on the can if you dont know how to do this).