Fuel system problem 89 Wolfsburg Cabriolet

I have an 89 Cabriolet Wolfsburg, 150K strong, Manual.
I have had an ongoing fuel problem.

The car will run great for an over an hour, then when I stop at a light it shuts off. If I shift, sometimes the car will buck like a horse, then when I step on the gas there is no responce. Sometimes it will not want to turn on after that.
I am sure the problem is with the fuel system. The only reason all of this happens is because the car is not getting gas; the gas petal becames unreponsive.
When this all happens I hear a buzzing noisecomming from the fuel pump and when the car is about to shut off it makes a high pitched whining noise.
I have replaced the fuel pump with a Bosch fuel pump and changed the fuel filter. So I am sure these cannot be the problem.

Besides this problem the car is great.

I hope you can help me.

THANKS

Without the proper tools to properly diagnosis this problem I would look at the in tank fuel pump if this particular vechile has one as the culprit due to the change in pitch of the fuel pump it sounds like a restriction. If this vechile dosen't use a pre pump i'd drop the tank and look at the sock on the fuel pickup for contamination and the possible cause of the restriction