Do a feel test. If the low side line (Bigger Line) is cold going to the dryer and the dryer is cold, Then the problem is in the mode doors! If its not cold, then you still gotta look at the pressures. If the pressures are good and the low side is not cold, then either a liquid line (where the orifice is) or there is too much oil in the system!

Another thing to try(sometimes works), is to disconnect battery for a few minutes. When you reconnect battery, sometimes everything resets and begins working fine. Worth a try...worked for me on my AC issue.

Cummins use an electric fan clutch. The tech who looks at it needs to look at the duty cycle of the fan clutch. If it is 85 % and the high side pressure readings are above 275 you have a problem.

The fan clutch was replaced about a month ago. Shortly thereafter the orifice tube was replaced. The AC issues have been ongoing since last October. Since then the Compressor has been replaced, The Mode Doors have been checked, The orifice tube replaced and the fan clutch failed catastrophically and was replaced.
If it ain't putting out cold air after the next time they get it, I'm headed toward the Toyota Dealer for a trade in.

I'm seriously thinking there is a clog in the condenser or the evaporator core is very dirty and freezing up on you. Read my post above.....

The shop owner suggested that's the next thing they check. The compressor was replaced last October. I think it was leaking.

When this happens does the air flow drop but blower still sounds like it going full speed? If the system is freezing the air flow out the vents will reduce or stop but you'll hear the fan still operating normal. I might have missed what year your truck is but if it's a later model like 2007 and up you might consider taking it to a dealer at this point. New ac system are still the same as forever mechanically but now use sensors and computers to control the operation. Some smaller shop equipment can't monitor those ac sensor to see what's happening at time of failure. If the evaporator temperature sensor is bad it will do what yours is doing. At the dealer we can monitor ever sensor in the vehicle to determine what is going wrong. Some people think dealers are expensive but if they fix it right the first time it can save you a lot of money in the long run.

Wha every you find out that's the problem please post it so we know for the next guy. I had two shop tel me it will cost about $200. buck just to tell me what wrong with mine, it's losing coolest.

Well as a ase master tech, (ask someone else...ase) with no known knowledge or vehichle type, brand ,I may have missed it, it obviously sounds like a low freon or weak compressor, hence when eng cold, no heat in radiator,condensor, it will cool, after a little eng heat not so much, so with no gauge reading, etc, ki da hard to tell, if we are talking suv with rear air, or a ford, a reman comp WILL NOT WORK PROPERLY. ... dodges just don't cool enough from the factory.. so with a little more info, maybe some gage readings, vehichle, etc, I'm sure couples team,myself, ot triton ,can lead u in a rt direction, A/C systems are fairly easy to figure out, maybe not the real new systems, but....

2008 Dodge 2500 6.7 Cummins. Compressor replaced in October of 2015. full of Freon. It's going in the shop on Monday for the last time. If it ain't right then, it's going somewhere else, like maybe the used car lot.

If the drain is working with those symptoms I would pull the dash and clean the evaporator.
You have to pull the dash back to get to the AC system and its a pain. While you're at it you might have them look hard at the heater core.

Its in the shop this week. I told them I wanted it back Thursday....With cold AC.

Anything resolved? What it was?

Pin hole sized leak in accumulator. Lost 1/2 lb freon. Accumulator replaced under warranty from original repair.

So the AC is still freezing up. Drove down from the lake today and by the time we got to Houston, no A/C. Took it to the shop. Compressor completely froze over. Diagnosis: Thermister. They are replacing it in the morning.