hi, i drive an 07 vauxhall vivaro van for work partially loaded, there are 10 fuel "bars" on the dash and i used to get 70miles plus out of each one but since the 18000 mile service i am struggling to get 60 even when the van is empty on a long motorway drive at steady pace. the tyre pressures are fine so i was wondering if anything else could cause the drop. i am losing 100 miles per tank now would appreciate any ideas, vauxhall carried out the service. thanks