1990 Caravan: it keeps falling off...

How many miles...could be the fuel pump sock is dirty. Check for ampage from the data terminal located close to the relays. You will need a DVOM and have it on ampage test. It plugs into terminal #1 & #6. #1 isn't too hard to locate sine #2 is empty and #6 is on the back of that terminal which is on the same side of #2 terminal. The ampage shouldn't be no more than 4.5. If it is pulling close to 7amps, The pump is going bad. Another way to test it is put a fuel pressure gage on the schader valve by the throttle body. Place it up by the windshield so you can see if while you are driving and see if drops off while this issue is happening. A good reading should be at least 37psi. Make sure that you have a new fuel filter on which is under the vehicle, passenger's side.