Anytime I have a unit that presents a lack of consistent a/c cooling, I first check the heater control valve under the hood on the passenger side. Not only should you check to see if the unit is functioning but also check the integrity of the vacuum line feeding it. I just had this problem with a buddy's truck where the valve had been replaced last year, I found the malfunction was the plastic vacuum line had broken

 

Start checking the cooling fan.

 

I would check the cooling fan as well. If you have air moving across the condenser and the AC is working, that means that the cooling fan isn't turning on to move air when at a stop.

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If you have torque pro.. you can monitor fan speed. there is a good chance your clutch fan needs to be replaced. Mine was reading zero sometime and would go between 0 and 550 at speed. My AC was doing the same as yours is. Replaced the Clutch fan and it is good to go now.

 

I had a similar issue with my cooling fan. When I went to go replace I found the wire had pulled from the fan side plug. No source for a new plug so I just replaced the entire unit and kept the old as a spare.

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yea the fan sounds like the culprit. i'll take a look and report back soon. thanks guys!

 

Also.. Scan for codes and see if you have a P0528 while your troubleshooting.

 

i ended up bringing the truck to the dealer. As the members of the forum correctly predicted: they replaced a leaking AC line and the fan clutch! the bill is around 1800 bucks. thanks very much for all he help on this. I appreciate it as always.