Drive it enough to determine it's "warming" then stop as quickly as you can and feel the suction tube see if it is good and cold. If not you have a refrigeration problem. If so make sure the vacuum/ blend doors in the unit are not dropping out. Remember, your vacuum is always less when driving.
Also some of the Mopar compressors had a suction pressure regulator setup at/ in the compressor. I don't remember just how those work but that could be a problem
Also, I doubt this would give you cooling at idle, but too much oil in the system will coat the evap and reduce cooling.
The above mentioned moisture in the system is a good suspect. What happens is moisture freezes at the metering point.....orifice/ txv because that is where "the cold" LOL happens. Ices up, plugs, warms up, melts, then works again for a short time and does it all over again.