All of the Postal Service vehicles (LLVs) were made by Grumman, but those don't get very good gas mileage (16 to 18mpg). 500 Postal Service LLVs were converted to electric drive in short route areas (I can't find any specifics though).
Canada Post contracted Solectria to do EV conversion work on two LLVs, which were then evaluated in great detail.
https://www.tc.gc.ca/innovation/tdc/...500/13528e.pdf
Grumman made a few stepvan models as well as a couple firetrucks.