Stalls then runs fine again for 20 minutes

I have a 1989 Dodge 250 van, 318 V8.
After running for 20-25 minutes it stops. If I turn the ignition immediatly it wont start but if i wait 3-5 minutes it will start and run again for 20-25 minutes. When running it runs very fine. Problem started about 3 weeks back, no problems at all for previous 6 months.
The time running is not depending on speed, slow or fast it runs for 20-25 minutes.

Plese help.

Are there any other symptons prior to it stalling, rough idle, miss, or hesitation? Does this year van have an electric fuel pump? If so, have you changed the fuel filter lately? Some electric fuel pumps have a thermo-switch and overheating of the pump will cause this switch to open and cause the very symptom yu describe. After cooling the switch closes and presto, it runs again until it gets hot. A clogged fuel filter will cause backpressure in the pump making it work harder and eventually overheat. Another possibilty if you have changed the filter is the sump on the pump itself. Pumps have a strainer on the inlet side to prevent sediment from getting into the fuel system and these can clog overtime from poor fuel quality to running the tank low.

Until it stops it runs fine. Very smooth idle and no miss or hesitation, answers good on throttle. Fuel filter changed 6 months ago (about 6000km/3700 miles) I have not checked the pump, will do that this weekend.

Over the last couple of days it has been worse. I checked the intake, the strainer was not clogged. I start to think its the pump that is worn. As an original part is too expensive (the equvalent of 150 us$) I have been looking at generic pumps but Im not shure what minimum fuel pressure is required. Anyone knows?

Problem fixed. Between the fuelline and the throttlebody there is a small pice of fuelhose. This was a bit to long and because of that it was bent and so restricted the flow. I shortened this hose and made shure there were no bends and now she runs fine again.