Car Troubles!! HELP?!?

[Racerx2]

Okay i have a ca18det swap done.. Its stock except for a z32 maf.. i had a stock ecu with an afc and the car ran fine.. i upgraded to nistune and my car starts and idles but when i put a load on it the car will sputter and s[it around 3k rpms..but it can get it to go past that. also if i step it to full throttle it just wants to cut and stall the motor... i've checked everything and cannot come up with a soultuion...