'96 chevy 2500 4X4 starting problems

I am having trouble starting my truck in the morning or first time in the day. Once the truck starts then it runs OK except that I have to hold the RPM up
until the motor warms slightly (less than a minute). If I pump the throttle like a carborator then the motor starts (but hard). I have a TBI and it has not given any trouble until now. I have also checked the fuel pump (runs ok) and installed a new fuel filter and engine temp sensor. Anyone help my out please.
Bruce
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