hi..i have a problem with my 97nissan maxima.here the problem when i press the gas pedal lightly it go smoothly but when i press it alittle harder it jerking.evry time i go over 60mph it jerking.every day i start up the car it run ok.but when i put in drive the car die.i have code say ramdom misfire and knock senor.i have a friend check out my car and he find out my vaccuum drop when he raise the rpm.he say i have a restricted exhaust so i remove the cat.converter and the car still do the same thing

Optional Information:
1997 Nissan maxima 3.0

Already Tried:
i have replace the cat.converter.spark,fuel filter,air filter.check the coil it ok