Unfortunately, this seems to be a swelling issue for hitches added to these vans without anyone from Toyota expressing caution. I too purchased my $30K 04 Sienna with anticipation to tow camper in future. All literature makes assurance this van can tow. Month later, per Toyota salesman, I purchased a U-haul, 3500lb rated, 2" hitch. With some light load camping items and bike rack(w/bikes), it continually scraped up slight inclines, that I couldn't even use the rack. The hitch occassionally scrapes totally empty on inclines with just family. The Uhaul rep said the rear suspension shocks are insufficient. Toyota said use factory hitch, but from above threads, that won't resolve anything and believe that hitch is only 1.25". Toyota also said there's no other towing package or beefed up rear suspension package offered.
I've been searching for a solution. An off-road company has entertained other customers with similar problems by offering rear air bags. He quoted $350 for manual fill, or $950 for on-board air compressor regulator. He stated with air added, it would eleviate any mild loading issues, and when filled, it would raise rear approx 3inches. I'm sure these added items will impact the ride. It appears this is my only option if I want to use this van for more than transporting people. For reference, link for product info is:
http://www.riderite.com/
I certainly believe this is a BIG design flaw by Toyota because the deep well for the rear seats was overlooked. There's no clearance or provision made in rear bumper area to allow a custom hitch configuration close to frame, like already included in some SUV's. I'll contact NHTSC as well. It appears Toyota won't be any help unless we all pool are COMPLAINTS. I should have stuck w/ an SUV, if made aware of issue.