I tow a 7000 lb boat with mine without issue. Check the trailer manufacturer website and you'll likely find that the tongue weight on boat trailers is supposed to be 5%-7% for heavy ones, but never more than 10%. I also threw a set of sumo-spring helpers on there and it tows fine. Have already done an 1100 mile round trip with it. Engine is definitely up to the task, but mileage is a little worse than my previous GMC Yukon.
Overall I am very pleased with the setup, but have my fingers crossed for an aftermarket air suspension to really dial it in.