Sick slant six stalling while driving

Hi All. I am looking for some ideas on my 71 Duster. It will start and run great idling, drives well and after about 10 minutes going down the road it will start losing power and will stall out while moving. Usually happens in second or third gear. It usually starts right back up. Sometimes I can restart while coasting and it will run a 1/2 mile or so and same thing happens again. I replaced the carburetor, thinking possible float issue but have the same problem. Also replaced the distributor cap and rotor to no help. I’m running a Holley 600 cfm carb, torque flight 727 manual valve body tranny on my 225. It also was converted to electronic ignition. I’m thinking fuel starving situation, possibly fuel pump but not really sure. Car was restored about 15 years ago and has never had any issues like this before. Thanks