lowrider72

hello forum. i am new and it looks like you pros have lots of experience with these engines. i just bought a datsun 72s pickup that has a z motor in it with a weber carb. i was told the truck needed a new fuel pump and ran fine untill 2 months ago. i replaced the electric fuel pump on the frame rail and am still experiencing what i feel is fuel starvation issues. the truck starts and idles perfect. since the new fuel pump it also revs great, no hesitation and full exhaust revving. the problem is, as soon as the truck is driving, it starts to bog and tries to die. the engine is running perfect unless the truck is rolling. i can even push the clutch and work the gas to get it revving again! i have worked on dodges, chevys, fords, and chrystlers, but know nothing about this 8 plug z or vaccum problems. so my question is, how do i check the manual fuel pump on the engine, what do i need to do to find the where the problem is and have you ever experienced anything like this? i believe it is a vaccum problem because the truck is perfect when it is not under load. can you recommend anyone in OR who can fix or help me fix this? thanks