Thanks everyone for the comments. In case it's the burrs I have ordered a new set. I'll post back once I've tested it out (along with a new set of beans and perhaps changing the pressure) to make sure anyone seeing this thread in the future benefits from some information.

If the problem didn't exist prior to the service on the gaskets on the machine, I think you should check that the gaskets are in the correct orientation. Pull the piston and double check that one of the gaskets isn't upside down.

I agree with everyone who says there isn't enough coffee puck resistance. The ideal boiler pressure on these is 0.8 to 0.9 bar, not 1.0 bar. That allows you to cruise at that pressure/temperature and use half pumps to bring the group to the desired temperature. You need to measure temperature at the group for consistent brewing, and that's easily done with a temperature strip. And the main reason for tamping is even distribution of grounds.