My Greenline has just had it's 20k service.  Before it went in, I was regularly getting 60-70 mpg.  It is now only showing mid 40's.

Any idea what's going on????

I've always noticed that myself immediately after service.  Are you quoting those readings from the MFD?  If so it will most likely have reset after the service so some of the previous consumption history won't be taken into account.  Well it does that on mine anyway and always takes a while to build up some miles and get a more accurate reading after a service.  Maybe try the old fashioned way as well calculating between fills and then you'll find out quickly enough.