Check the oxygen sensors. that could cause it to run rich when cold. also I had a similar problem with a truck I had. The problem was the ignition coil, that's also worth a look. one last thought would be the catalytic converter. hope you find the problem.
'98 Jeep Grand Cherokee 5.9 Limited.
Mods: K&N FIPK, Viper Alarm, Air horns, Kolak Ignition Upgrade, Edelbrock IAS, Tint to match back.
Stereo: Pioneer Premier DEH-P840MP head unit, Kicker 12" XPL sub, Infinity kappa 6 3/4 in front, infinity reference 5 1/2 in back on stock infinity amp.