hard initial startup on 82 k-10

[4x4orbust]

hey guys, new here, i have a good question for you.
recently acquired a new (to me) 1982 k-10 with a swapped in 350.
I have it running good once it warms up, but when you first start it, seems to run off only 5 or 6 cylinders untill it warms up a bit (usually 3-5 minutes)  I'm not sure what the problem could be.  i have replaced the cap and rotor and thought that would have resolved the issue, but it is still there.  i have replaced all spark plugs, wires are good, and  once it warms up, it runs like a top.  doesnt smoke, bog, or anything.  i am thinking that the next logical thing to look at would be the carb, but how can that have this affect on the engine?
  i should mention that the motor and tranny were rebuilt  by the previous owner.  350 was bored .030 over, and the tranny was rebuilt at the same time.  (they only have about 2000 miles on them)  anyone help on this??
thanks!!

[Captkaos]

What is the status of the carb?  Any leaks?  Does it have a choke?

[VileZambonie]

Make sure the choke is closing and fully opnening

[4x4orbust]

not really sure what kind of carb it is, but it seems to have an electric choke on it. i can get pics tomorrow.   there are no visible gas leaks and no air leaks.  i also forgot to mention that the truck sat for 2-3 years before i got it.  i checked the choke operation earlier today, and when the engine first started, it was closed, then after a minute of running was not fully open, only at about 20 degrees from horizontal.