I have a 12' Coleman Utah pop up camper that I pull with a '96 Royal Exceed. Trailer is somewhere between 3000 and 3500 lbs. It's also big and wide, meaning it punches a big hole in the air. I've pulled it for 3 years now.
It is probably too much trailer if you are towing a lot. You're limited to about 105 kph, and it is going to take some time to get to that speed.
The past 2 summers, the trailer has been a handful, with sway coming in anywhere between 85 and 100 kph. This summer I put a lift on, and i don't know if it's the stiffer springs or the new shocks, but the sway has gone away at least to 115.
So, try to stay at 2500 lbs. If you're going to go above this, here's what i'd do:
1. EGT gauge. It's easy to get into high EGT's when towing
2. Turn up the boost with wastegate spacers, and wire your pressure relief valve closed. The power difference between 12 psi and 15 psi is wonderful.
3. Either fix your suspension with new shocks and/or a lift or helper springs, or use aweight distributing hitch to keep the van level and the sway away.
Here's a picture from 2 days ago. Towed about 4 hrs from Niagara to Minden. With the new boost and the sway gone, it was the most pleasant tow I've done.

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