Fuel And Starting Issue 95 Jimmy

Changed the motor put a 4.3 vortec back in it.. new motor has spark. wont pull fuel from the gas tank for some reason. will start if you put fuel in the intake.. but other then that it wont do nothing like its getting no gas any ideas.. changed everything on the intake also even the spider and retimed still the same issue.. thanks did u test for fuel pressure at the rail with a pressure gauge? Is the Car Repair Talk's forum.