I have just returned from a trip to Wyoming in my 1980 Westy and my gas
mileage, as it has been for the last two years, was a stunning 13-15mpg
depending on the direction of the wind.  The engine on this van was rebuilt
(rings, valves, new hydraulic valve lifters, one new head) 25,000 miles ago
when we dropped a valve seat, again in the magnificent state of Wyoming. 
The compression is good all around and the plugs look a beautiful toasty
tan when you pull them out.  The engine seems to perform adequately,
although it has no oomph at the high end;  that is, if you punch the
accelerator at 55mph, not much happens for the longest time.  When the
engine was rebuilt, the mechanic had this idea that the engine had
overheated because it was running too lean.  It had the rotting remains of
an EGR system on it at the time which he tore off and plugged up, insisting
it was a potential air leak. Is it possible throwing out the EGR system
screwed things up royally even though the plugs would seem to indicate that
the fuel/air mixture is not out of line?  Anyone out there with similar
experiences and possible cures?

David