98 K2500 electrical gremlins-help needed

[rickpilgrim]

This has been going on and off for 2 yrs and for once I'm at a loss.

First- when you first start the truck the complete(gauge doesn't show it) electrical system seems to "pulse". Lights get brighter/dimmer heater fan faster/slower anything electrical has this problem.
Now I've had 3 new alternators and 2 new sets(dual battery plow truck) of batteries and done numerous electrical checks for shorts, opens grounds and no change. After 10-15 minutes everything stabilizes and acts normal at 13.9v on gauge and multimeter. ECM????
Second- when below 40 degrees if left overnight when you first start it it will be between 8-15 min before you can shift out of park. New shift cable didn't change it, new column from Tahoe no change, 2 -4L80E makes no difference.
Add that to the new fuel spider and regulator that acts just like the leaking one and no check engine light or no codes set even when smoking black under full throttle really make me wonder.
Ideas anyone?