I can attest to a 3.5l eco. I can drag 5000 lbs up and down 12000 mountain passes with zero effort and the trans never sees temps over about 220, under 240 with 95degree outside temps.

Mind you that EXP XL Max is actually tuned from the factory, buck like the SCT Performance tune. It also has one temp cooler plugs in it as they knew that a tube would need it. Course that mandates Super unleaded ONLY.

But a super duty would be a much better choice for this. The 6.4 is a solid platform. Tune it with a banks 6 gun and have no issues. Put a camper top/snug top, and then you have an suv storage area, and seating for 4 comfortable. Many used 6.4 have truck toppers. Note: replace all the front end bushings at 100k. Get rid of it at 170k. They start to just have maintenance issues. Change the fuel filter (both including the frame one) and service the transmission by dropping the pan and putting in a new filter.

Then 150k towing is no issue.

But if it’s not obvious I have been there, owned many of what you are asking and battled the problems, then yeah get a Chevy of that age (motors are junk for towing with GM in those years) and enjoy your battles.