I live in Texas and it's been right at 100 degrees lately. I have the original AC system with no modifications and it cools the truck fine. It sounds like you either have a leak or a problem with the compressor.
The best way to cool your truck: Start the truck and roll down the windows and turn the AC to MAX and the fan on high (always turn the ac off before turning the engine off). Drive with the windows down to get some of the really hot air out of the cab then roll them up. Leave it on MAX and adjust the fan as the cab cools down. If it's really hot or really hummid, leave it on Max, otherwise switch to regular AC. All the Max setting does is circulate the air in the cab. Switching to the regular AC setting just brings fresh air in from the outside. Contrary to popular belief, Max doesn't use more fuel or anything like that, it just controls if the air in the cab is recirculated or if fresh air is added.
You should be able to have an AC shop check out the system and add some R134 if needed for $50 or so. If it needs a lot or refrigerant or if there's a problem with the compressor, it can get expensive really fast.
If you are good at DIY and following instructions, try what dhvaughn suggested. You may be able to check the pressure of the system with a tire guage. If you add more than one can of refrigerant, add a can of compressor oil and consider using the refrigerant with the dye so you can tell where the leak is.
The big safety concern is hooking the can up to the wrong fitting and blowing up the can. Adding the refrigerant incorrectly can also ruin a good compressor. Unless you plan on doing a lot of studying and fixing any problems yourself, I'd just take to a professional and have them check it out.
AC work isn't hard. You can do pretty much everything yourself including replace the compressor but you do need to do a lot of learning before getting started.

 

The high side and low side connections are different sizes. Sailor proof. Go to harbor fright tools and get an a/c gauge set for $34.95. Check and see if the high and low end are under the correct amount of pressure for the ambient temp. For example if it is 88 outside your low side should be 40-45 psi, and the high side should be 225-275 psi. If they are both low add some freon. The gauge set has a little chart to guide you through the troubleshooting process.

 

Sailor proof--lol
By the time he spends $35 on gauges and $20 on R134, the shop could tell him if topping it off with refrigerant is going to stay charged for two weeks or two years. Unless he plans to fix it himself, I'd go to a professional. If he's comfortable troubleshooting it and replacing parts and downing some reading, buy the gauges and go for it.

 

Most of us here at Dodge Forum like to do it ourselves. I have three vehicles, so the gauges come in handy pretty often, and there is at least 2 neighbors who are glad I got them. The last time I took a vehicle into the shop for my A/C it cost me $300 to find out I had a leaking schroeder valve.

 

Would the compressor oil make a difference in cooling also? And i do have to hoses to add the freon to the system but they don't have gauges on them

 

Compressor oil will keep your compressor from burning up.....

You really need a gauge. Just 'guessing' at how much charge you have is a recipe for disaster. There are cans of refrigerant that come with a hose with a gauge.

 

$300 for a Schrader valve is off the chart. That's a 50 cent part. Even considering vacuuming down the system and refilling with refrigerant that's crazy.
I'm not trying to dissuade him from doing it himself. I said ac work isn't that hard. I just think it's a waste to buy gauges just to see if it needs r134 and then end up paying a shop to replace the compressor. I replaced pretty much the entire ac system on my mercedes so the cost of the tools was justified.
Heyyou is right, you need a gauge and you can get a can of r134 with a gauge tied to it from Walmart for about $20. You need to add the oil because if you have a leak, oil leaks out as well as the refrigerant. It's a common mistake for someone to keep adding refrigerant but not replace the oil and the compressor burns up when they could have replaced.
Jamin Ram, if you are up for it, buy the can with the guage, see how much refrigerant is needed and post back. I'm sure we can walk you through it.

 

If you have some way to recover the freon , If you haven't checked the orificeTo filter, it could be clogged.I did an AC job today the orfice tube was so clogged it was coming apart..the ac would go down to 60 but would stop cooling when you started driving. My dodge was 3.95 the ford i dod today cost the same ,3.95 for filter but some cost as much as 40.00.take the old one with you some take different ones for same truck.color coded white ,green red .The truck from today down to 49 degree . Good luck

 

OP probably got his problem solved one way or the other. When replying threads/posts, look for a date. You replied to a 12 year old post!

 

hey nothing wrong with replying to a 12yr old post, when people are having similar problems. It just adds to the info on the threads. Ive done the same, in hopes someday it will help someone down the road! Cheers!