I have a '87 300 SDL with a interesting cruise contro problem. When the air temp is above 55 degrees the cruise control works OK. If the temp is lower thena 55 the cruise control works intermittently and often activates only by using the deceleration control. Any thoughts?

Sure, thermal creep. You will need to have the cruise amp pulled and checked for cold soldered joints. When the amp is warm, ie. above 55, then the intermittent contact is not a problem. When it is cold, the metal will contract and produce open circuits. Of course, having said that, make sure the actuator connector is firmly seated and not corroded..