Yup, I second everything Dan said.
And check the big black plastic air hose from the Air Mass Meter to the intake for cracks or holes. Any vacuum leaks here result in improper mixture.
If you want to be sure about the problem with the fuel pumps, a fuel pressure gauge on a tee with a long hose can be installed in the fuel line, and the gauge passed up under the hood so it's visible in the windshield. It's kind of an odd rig but it will help you verify that it is indeed fuel pressure, or that it's something else.
Other less likely but still troublesome vacuum leaks can occur at the intake manifold gasket or injector seals as well- if nothing else helps, those are at least not expensive parts to try.
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Rob Bareiss, New London CT ::: '87 244DL/M47- 230K, 88 744GLE- 220K, 82 245T-181K Also responsible for the care and feeding of: 88 745GLE, 231K, 87 244DL, 239K, 94 855GLT 189K