Sounds like a lean condition. Obviously, your temp gauge should be reading cold and less air is used for combustion or extra fuel should be getting added. Maybe the temp gauge is reading right but the computer is getting the signal for a warm engine instead of a cold engine. I don't know what parts are involved.
1992 Tbird LX 5.0, 3.73 gears, 1995 Cobra intake, deleted air silencer, 2.5" mandrel bent dual exhaust, SCP shorty headers. Updated four-hole fuel injectors. SK shift kit in AOD. Vogtland 0.9" springs, Tokico and Bilstein shocks.