Strong odor outside car but coming through vents

After a nice long drive, shut it down and raise the hood.

Do you see a hint of smoke coming up around the engine anywhere?

If so, it may be a small oil leak from a gasket somewhere burning on the exhaust.

Have you had anyone "automotive" oriented to look at it? Even an experienced auto parts guy at a parts store might give you a good idea of what it is or where it might originate from.

What about the shop that did your engine/transmission swap, surely they would stand behind their work?

Sometimes smells are deceiving depending on the type fluid that might be burning, someone around the smell all the time might pick it out in a second.

I once saw a decaying chipmunk crammed in a tight spot under a hood being blamed for numerous fluid failures/burning rubber parts/carbon monoxide/etc. It indeed had its own unique smell in an automotive environment. After it was removed, we were surprised that flies were not present and pointing it out.

Normally, gas smells like gas, if you suspect that is what you smell, I would not put in the garage and I would cease driving it until you get it fixed!

Keep us posted.

The Medic