OK, haven't gotten a gauge, yet, but did check all the vacuum lines for blockages ... no blockages ... had some extra nylon hose on hand so replaced 'em.
I replaced fuel filters a couple of years ago .... will give it a shot in a few days.
Thanks to everyone for their help.
1991 350 SDL (200K and she ain't bent, yet)
former 2002 E320 4Matic Wagon - good car
former 1985 300 CD - great car
former 1981 300 TD - good car
former 1972 280 SEL - not so good car
a couple of those diesel Rabbits ...40-45 mpg