Paul, check the vacuum line to the upshift delay valve, make sure it's connected, it might have slipped off.
If the pump is making noise, it could be on it's way out, but since they only run a short time it should continue to function for a while. It also has a vacuum line that has vacuum only when the engine is cold (through a thermo switch).
You just had the head worked on, is it possible some vacuum lines were errantlt routed or otherwise misconnected?
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72
'02 CLK320 Cabriolet - wifey's mid-life crisis
2012 VW Jetta Sportwagon TDI...at least its a diesel
Non illegitemae carborundum.