1995 Mitsubishi 3000GT 3000 gt DOHC 6g72

I have a 95 3000gt 6g72 non turbo dohc I had the motor replaced three weeks ago water pump, timing belt, plugs, wires, ecu temp gauge, coils, top vacuum lines excluding purge container lines, plenum gasket, stepper motor. Also took to a shop for a standard diagnostic and they could not find any flaw in the running condition. But I have a slightly rough idle with no lights also when start it when cold it goes to 2500rpms for about 2 minutes before coming down to around 1000rp-800 rpms its a steady idle speed with a sputter. Also if driven while cold it act's like it doesn't want to really go almost like it wants to stall or something without doing so!But when hot drive fine little power loss if any just the funny idle!Please help!Thax in advance