Car jolting like kangaroo

[sr20det]

so i replaced my centre peice muffler as it was cracked and crokey and sounded like ****.
after replacement everything sounds great until you push the pedal lil more then 10% it starts bouncing back and forward like its struggling
my tuner has been a **** around. before muffler apparently my crank angle sensor was faulty and sometimes i had problems starting it so he plugged in his laptop few times changing fueling etc on the spot for the nistune ecu. The way it jolts back and forth i believe its something to do with the fuel..
i can see the revs racing to red line but no pull with it its really strange any ideas? I have new nismo 740cc injectors less then 1 month old so i doubt its the injector flow?

 

[Auss15]

I assume you had a retune after the 740's were fitted ? If the CAS was faulty did you replace it ?

 

[sr20det]

I assume you had a retune after the 740's were fitted ? If the CAS was faulty did you replace it ?

everything was in before and tuned on the cracked centre piece muffler, over time it got really worse so i recently replaced it. The CAS was replaced yeah with a second hand one apparently cause they too expensive new and 'i wouldnt want to spend that much' my tuner says.. nothing was wrong with car before replacing the muffler now issues started.. i should note the car was tuned with a bad hi flow centre muff piece but not after replacement