[Ginola]

I would never buy something that's failure or poor running can cause total failure for your engine from an unknown on eBay.
The 3" exhaust system at your power level is overkill really and will have lost you a little mid range torque for the sake of 1 or 2 more hp at the top of the rev range.

Also if mapped before and then you changed to 3" system without a map tweek would make it run leaner at the top as your flowing more air.
Hopefully Duncan will sort it out for you, I would be driving off boost until it's sorted, a good aftermarket fuel pressure regulator would be a very wise investment.