Choke thermostat /RAGE

at idle in drive, your voltage is probably too low...

make sure all electrical connections to the alt, battery, ballast resistor, voltage regulator are clean and shiny and nothing is loose.

then... i bet you will have a smoother running idle while in drive.

by clean and shiny i mean using light grit sandpaper on the connectors where possible, sometimes you have to use a knife tip to scrape the tarnish off if you cant get to the connections with paper. also make sure the alternator is grounded well, and that your engine is grounded to the frame and to the firewall.