I dont know mate, why would the engine feel like its lost all power, almost as if the exhaust gas cant escape quick enough, It did happen when I had a stock exhaust too.
The carbon on the bumper was roughly the size of this comma , but flecked all around the tail pipe area on the bumper.
Traction control works in various ways, it can brake on some of the wheels, it also can reduce the spark to one or more cylinders, or reduce fuel to cylinders, so you would feel the engine "lose power". some cars (if fitted with drive by wire) can close the throttle, and turbo engines, the boost solenoid could be actuated this then reduces the boost, and reduces the power.
I dont know what system nissan use, but most cars that i have worked on use the braking to some of the wheels, which work with the ABS.
from what you say it does sound like TC kicking in, ive had this before, its annoying, but ive only had it when changing gear very quickly, and usually from 1st to 2nd.
hope that helps.