An o2 Sensor won't give you a misfire that quickly.
I'd very very worried about the people working on your vehicle.

Air mass meters have a tendency to fail and give very low power with delayed upshift. They don't leave fault codes relating to amm's, they do create codes relating to o2 sensors.

Disconnect your amm wiring and go for another drive. If it's better then it'll probably be your amm at fault

__________________
Alex.

MB Tech
Sydney, Australia
Volvo 122S
W201 190D 2.5 manual
W202 C240
W203 C32