Check the wires to O2 sensor they might of damaged one. Or a joint is out restricting exhaust other wise i have no idea.

Or take it back and jump up and down and shout

Possibly they have damaged the probe and the brain needs reset to get it out of a limp home mode
_________________________
P.Allison fixer of big engines Mk2+Mk2a signed by God / Hacked by the Lord Aberdeen Scotland