Hey guys I have a 2001 Xterra 4x4 with a JDM motor installed with 55K miles and every time i drive it uphill it cuts power and sometimes turns off however 1st and 2nd gear seem okay at lower speeds. I have this problem past 40 mph. So i been reading online and calling some mechanics around town and they claimed it bay be the O2 sensors or the catalytic converters. Thus I bought new O2 senors and new cats and installed today and same thing is happening. I did the motor swap myself with a help of a master technician. We cant seem to figure this out. Also I had an aftermarket intake kit on but i recently bought OEM intake from a junkyard. I have been reading a lot online and most people claim it was their catalytic converters. I checked my TPS sensor with a volt meter and it seems fine. I havnt checked my CPS, but wouldnt it throw a code with a OBII computer?? Is my tranny the issue or my torque converter?? Has anyone had this issue and fixed it? I feel like its something so simple. I have NOT checked the fuel pump too but that should throw a code! I am going crazy, please help! thank you.