need some carb help...I think

[67sss]

Have a 72 gmc, smog stuff taken off, 350, auto and am having issues with the carb. I've adjusted the idle mixture screws out to the starting point of 1 1/2 turns, set idle at 600rpm, and the hi idle at 1000rpms. When I start it each morning,this only happens when the engine is cold, I step on the throttle to set the choke, start the engine, it runs for 10-15 seconds then dies. I do this same procedure 4 times and usually on the 4th time it stays running. Also as I drive the engine seems to be starving for fuel, I need to "feather" the throttle to keep the truck going. Thanks in advance for your help..Oh yea, this engine originally came from a 75 4x4 GMC 3/4t auto truck, and the motor is a GM crate motor.