Did you reuse the gasket when you swapped the turbos? That could have caused that problem...always best to replace gaskets that are in very high heat area's when swapping parts.
The very reason I aways recommend to change the Gaskets especially being close to 500 deg exhaust heat!
Definitely would of thrown your Fuel trims off!
Glad you caught in time. Z
Yes, that could very well be true. Just like Ford says with wheels, checking the bolts a couple hundred miles after install is a must. Dunno if loctite would have helped any.