A MBZ dealer tech told me to bleed the injection lines at the fuel distributor (be careful of raw fuel spilling over a hot engine!) and a lot of crap came out. I actually did this twice. It seemed to help quite a bit.
You said you "checked the fuel filter and fuel pressure" .... a clogged filter will definately slow you down.
On a long shot- you could pull the fuel tank sending unit and take a look into the the fuel tank.
Whats the history on the car?
'03 E320 Wagon-Sold
'95 E320 Wagon-Went to Ex
'93 190E 2.6-Wrecked
'91 300E-Went to Ex
'65 911 Coupe (#302580)