You're best bet is in drive with eco off. The ZF8 has around 40 shift maps that are selected based on driving style, engine load, and drive mode. When in drive with the cargo area loaded or towing a heavy load the transmission will respond accordingly.

I do put it in sport mode when descending a steep grade while towing as it will hold a higher gear.

 

I pull a couple jet skis throughout the summer and it is the only time I actually use SPORT mode. Always seems to find the right gear especially in hilly areas.

 

Sounds like we have the same setup! I have a 3000# empty weight travel trailer as well, and a 14 v6 Laredo...though mine only has 50 couple thousand miles on it. So far, only towed a few times locally and one 700-mile round trip last summer. I pretty much always turn off ECO every time I start the thing...otherwise it seems to be behind the power curve. I found that towing it handles well with ECO off, I don't think I ever went to sport mode. I did however end up manually shifting it a lot of the time so I could better control exactly what it was doing and keep it from up or down shifting too much, as well as downshifting as I came to a stop. I would play with it and see what you're happy with, I don't see anything being a problem other than if it is constant down/up shifting on the highway or in hilly terrain. Highway, probably fine with ECO off as long as it's not constantly shifting up and down for every little thing, in which case just lock it where you want it and let it roll. I could see where in some circumstances sport mode might work nicer, especially if you're not manually shifting.

Wesley