If it isn't the gas--What is it??

[MBZ86]

Hello, 1986 420 sel
The car has set idle for about a year and would not start. I discovered that no fuel was getting to the engine. Assuming that fuel could be ransit and possible blockage of tank screen, filter, lines etc, I drained tank , blew out the tank screen the return line from engine to tank.

I replaced both pumps and the filter. I flushed out the incoming fuel line to replace the old gas with new before trying to start it again. Within 4 or 5 cranks, with the help of a little starting fluid, she started up and ran and idled fairly decently.

After warming it up I decided to give it a test drive around the neighborhood. I took it very easy to begin with allowing it to shift through all the gears etc. As I gradually tested it a little harder I found that at about 2500 rpm's it stalls and dies. It will start right back up with ease.

In order to get it over 2000 rpm's I have to drive it in its lowest gear (only b/c of speed limits and stop signs on the street I am driving it on).
In addition, at what ever speed or rpm's, if I rapidly depress the accelerator it will also stall and die.

I believe that everything from the tank to fuel distributor is in good working order. I have not touched the fuel distributor or anything beyond. Could it be that the distributor is gummed up from the old fuel that has been sitting in it for so long? or ?????

What do these symtoms indicate from your experiences?

Thanks for whatever suggestions you can offer!