Auto Air Conditioning & Heater Repair: 1998 DODGE RAM 1500 5.2 4X4 A/C PROBLEM, thermal expansion valve, dodge ram 1500

Question
I JUST HAD MY EVAPORATOR AND DRYER REPLACED ON MY TRUCK AND WHEN YOU ARE SITTING AND IDLYING THE AC GETS GOOD AND COLD BUT AFTER GOING DOWN THE ROAD AFTER 10 OR SO MILES THE AC STARTS GETTING WARM AFTER SITTING FOR A WHILE IT WILL COOL AGAIN FOR A WHILE I REPLACED THE CLUTCH KICKOUT SWITCH AND THE HIGH PRESSURE SWITCH  DO YOU KNOW OF ANY REASON FOR THIS?

Answer
 Are you sure you have the correct amount of refrigerant in the system?  Did you replace the thermal expansion valve at teh same time as the evaporator?
 What are the pressures when the system starts to blow luke warm air and is the compressor turning off or still running.
 Look closely at all the lines on the car when it stops working.  Is one icing over or getting frost on it?

Wayne