well on my 240D i have little over 2k on my monarks and they seemed to be no differance than the origional ones .

just put monarks in my 617 powered mazda .. havent compared mialage but IT runs a lot better at slow Rpms now ..

at 220k i would suggest your timing might be more the problem .
could be 1 or 2 deg off

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current fleet
Ford f350 dully 7.3L 1990 . ats turbo , zf5
Mazda 4x4 b2600 with 617 20-26 mpg
Past fleet
1983 240D w123 232k 25-30 MPG
1984 Ford f250,1979 ford 150 300-6 (sold@ 251K )
81 300D, 79 240D , 2x 76 300D ,74 240D , 2x 89 grand prix , 85 grand fury , and several other fords

Custom machine shop work ..