1981 Toyota Pickup 81 Pickup Put Rebuild 22r N Hit 500 000 Rebuilt Amotor

I have a 81 Toyota pickup. I put a rebuild 22r n it when it hit 500,000. The rebuilt amotor has about 50 000. For the first month our so it ran fine. Now it only wants to idle half the time.when i first start it it runs fine and idles high until it warm and choke kicks off.and it spits and sputter at about half throttle. I was thinking maybe its the fuel pump. Seeing that its mechanical maybe its not about to pump enough fuel because its wore out.