I have a couple ideas for you.
First, you might have a plugged up catalytic converter. A good way to tell is to remove the O2 sensor from the front converter and start the car. If it keeps running, then it's likely the converter is blocking the exhaust flow, and removing the sensor gives the exhaust a place to go.
Second, it is possible there is a problem with the timing. If the belt jumped time a few teeth, then the car won't want to stay running. To test for this, either pull the timing cover and set up the alignment marks, or sometimes a compression test will point to the problem.
Finally, take a look at the large vacuum lines back on the passenger side of the throttle at the back of the engine. The breather tube as well as the PCV valve live back here. If one of them has split or broken off, then the engine will stall due to a large vacuum leak.
These are the areas I would look at next since you have done the fuel pump and checked for codes.
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Thank you so much!