91 Somoma 4.3 w/cold start problem

I have owned this truck since new in Aug. '90 and proud of it!
Only have 108,000 miles on this 4.3 and few problems up till moving to North Carolina from Indiana in Sept.
Trouble lately has been cold starting for initial 10-15 seconds...
Very rough, then smooths out fine. Just tuned it w/new fuel filter, pvc,O2 sensor, maping sensor, and computer chip installed. New cap,rotor,plug wires, and pressure check on fuel system states fuel regulator is operating at correct pressure and fuel pump is working.
The problem has not gone away. But once it warms up and engine smooths out, it runs strong!
What could be the diagnosis? Is the gas down here different than in the midwest? 87 octane is recommended and has been used since new.
Help if you can...

Brian in Charlotte!