I would check the fuel pressure with a quality mechanical gauge, the best being a low pressure GM TBI gauge (0-15lbs) plumbed in at the fuel block and taped to the windshield during road test. If the pressure does drop, you need to find the cause, whether a bad pump, vapor lock as mentioned or the system drawing air before the pump (dried out rubber fuel line section).
It may be something as simple as sediment in the tank blocking the pickup filter after running awhile. Where is your inline filter?
[ March 04, 2003: Message edited by: KULTULZ ]</p>