you have a fuel delivery problem pure and simple. i would NOT throw one single part at it before you receive your cable and software and take a look at the ecm unit....specifically diagnostics section and stored historical codes. you're going to find that you have several including but not limited to 13,16,23,32. a fuel delivery problem may involve a lazy/failing O2 sensor but in all probability your gremlin lies within the fuel pump assembly.....internal connector hose...failing pump...PR unit.....sock filter. below are the fault codes for your year XB. hang onto them for diagnostics when you run same. and the reason that you can pull in the clutch and "rev" the motor with no problem is that there is no load on the motor during that maneuver. no load means minimal fueling demands. the decel pop quite common with stock mapping and that ear piercing exhaust you're running.
The trouble codes are as follows:
11 Throttle position sensor
13 Oxygen sensor
14 Engine temperature sensor
15 Intake air temperature sensor
16 Battery voltage
21 Interactive muffler control (XB12 only)
23 Front fuell injector
24 Front ignition coil
25 Rear ignition coil
32 Rear fuell injector
33 Fuell pump
35 Tachometer
36 Cooling fan
44 Bank angle sensor
52, 53, 54, 55 ECM failure
56 Cam sync failure