[V8] 90 V8 Has Nazi Gremlins

[Jeff Bailey]

Ok, it's been awhile since I've posted anything, but this one has me 
stumped.  Car will start and run perfectly for exactly 15 minutes, then 
it's as if some little Hitler turns the key off.  No stumbling, no 
surging, no anything to indicate loss of fuel, just as if I turned the 
key off.  This happens regardless of engine speed.  What could possibly 
be possessing this thing?  Thanks in advance.

Jeff B

90 V8 Quattro 106k miles
95 Volvo 960 113k miles (gets driven more because cheaper/easier to fix)