Are gas caps universal

The caps are not universal, there may be a cap that fits multiple makes but not all. For your Caravan the Stant number is 10838. That number doesn't fit any GM models though.
It is possible to test the cap, however the time it takes for a shop to test it would likely exceed the cost of a replacement cap. To look at it visually you want to look at the rubber gasket marked with the arrow. It should be soft and pliable with no cracks or damage. Then look into the filler neck for any rust or dirt in the area the cap seals. Rust or dirt there will cause a leak. I have done a band aid repair on them if they are rusty, you use some fine scotch brite material to scrub the rust away then put a couple coats of paint over the rough area.
A common leaking point on the Caravans is the filler neck itself as they rust through and leak in the area between the tank and the fender. For that a smoke tester would be the fastest way to test for a leak.

Hi Steve! Thank you for your speedy reply. Especially so i can be right by an expert! Haha. The gas cap he put on there shows no ware or anything in fact it's brand new looking as it is. What i'm concerned about is keeping this one versus what you said to just get a replacement. Figured i would be able to find that # printed on the cap..
i do have another question (related) that Google failed to acknowledge. That is if these 3 obdii codes have anything to do with each other? I have researched them.. 2 EVAP leak codes one small one large. from the ECM and the EGR system failure. I know how this troubleshooting goes.. Extensive. I just want to be looking in the right direction. I do know the EGR has to do with gas and flow so it's similar. I am thinking with the gas shutting off every time i pump, plus today i noticed liquid (gas) right outside the filler spot. Sounds like my filler tube has a leak also would explain the gas smell even after fueling. Am i on the right track Steve? You guys are awesome. Thanks for the posts and all your help!

The EVAP codes for large and small leaks are generally caused by leaks in the fuel system. Things like a vent solenoid or in this case a filler neck leak that are not sealed. The testing on that system works like this. You start the engine, it checks that the parameters are within the correct ranges and it starts the EVAP test. It shuts the system vent solenoid and opens the purge valve. The ECM then starts a timed test. It looks at how long it takes for the vacuum through the purge valve takes to apply a set amount of vacuum to the tank. Then it closes the purge valve and starts counting how long it holds at that level and then it opens the vent. If it takes too long to pull the vacuum it sets a code, if it leaks while sealed it sets a code and then once it opens the valve it can also set a code if the vent doesn't open properly. All of that is to be sure gas vapors don't escape into the air. Gas smell and dampness would both be good clues you have a leak.

Now EGR is a different system, it is Exhaust Gas Recirculation. It is a valve and passages/tubes that are used to send exhaust gas back into the engine to help control exhaust emissions and combustion chamber temperatures. A code in this system won't be related to the EVAP codes.
Could you post the exact code you have for the EGR please? As well as which engine you have?