Automotive Air Conditioning Information Forum

i have a 2010 T800 KW that is not cooling sufficiently while driving down the highway. Mechanic has replaced all of the components in the system, vacumed for 1 hour and charged with 54oz of 134. it works perfectly while in the shop. As you travel down the hghway it will intermittantly cool. When i say all components i mean everything except one hose. Any thoughts?

Does the vent air flow stay the same when it stops cooling, or does the airflow from the vents decrease when it stops cooling?

Given that a truck that old should have about 550,000 miles on it by now, it could be electrical or the refrigeration loop.