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According to what I saw the Ram Promaster 1500 can tow 5100 lbs "properly equipped". Be sure the one you're thinking of buying is "properly equipped". The max trailer weight of the 174 is about 3800. So, you should be OK if you don't carry too heavy a load in the van. That's because tow capacities are usually spec'd with the tow vehicles unloaded and only the driver in it.
Do this. Look at the driver's door sticker of the new van. Find the MCGVWR (max combined gross vehicle weight rating). That is the total weight the trailer + van + all people and cargo can weigh. Take the curb weight of the van(about 4800) and add the weight of all the "stuff: and people that will be in it, and add 3800 to that for the trailer. If that total is less than the MCGVWR you should be OK.