A/C blows warm only at low RPMs or at idle, blows cold while accelerating?

Thanks for the input. I had a chance to look at the truck a little more and noticed that the compressor was kicking off and on constantly, probably every 20-30 seconds. Normally I would have thought that meant low refrigerant, which I suppose it could be, but that would mean a fairly significant leak, since the system was fully charged very recently.

Hi Joe. I spent some more time trying to diagnose my A/C today. One thing I should mention is that I am hearing a loud hissing sound that gets louder after the A/C is on for a few minutes, and the hissing continues for about 30 seconds when the engine is turned off or when the A/C is turned off, and slowly dies down. I'm not sure if the hissing is the actual sound of a leak, or if there is anything else that is malfunctioning in the system that could cause the sound, but the hissing is definitely related to the A/C in some way.

I also noticed that the condenser fan is not turning on. I assume that at idle, when the A/C is turned on, the condenser fan should come on immediately, but it does not seem to ever come on.

Here are my A/C pressure readings:
All readings are with engine running.

When the A/C is first turned on, the A/C quickly jumps to about 200PSI, but within a few seconds it is rapidly climbing, and within 20 seconds or so it is all the way up to 400-450PSI, and pretty much maxes out on the gauage. The low side is holding steady at 58PSI with the A/C turned on.

When turning the A/C back off and letting it settle for a minute or so, the low side is maxed out on the gauge, which is about 130PSI, and the high side sits at about 140PSI. The previous time that I turned off the A/C, the high and low side went to about 125PSI, so they seem to be consistently sitting at the same PSI as one another when the A/C is turned off.

It was around 55F when I checked the pressure, so not hot at all.
I will check the static pressure and record the sound for you.

Fixed. The issue turned out to be the condenser fan. It was completely dead and no longer came on at all. I stuck a box fan right in front of the condenser and ran the system, and the high side pressure immediately began to rapidly lower, as much as 150-200 PSI, and the A/C began to blow cold.
As soon as I would turn the box fan off, the high side pressure would quickly rise back up to 400-450 PSI.
This also explains why the A/C was able to blow cold when the truck was moving, since the natural air flow was enough to cool down the condenser. The loud hissing seems to have been a symptom of the high pressure in the system, due to the condenser overheating.