I called Toyota National and spoke with a representative, not my local dealer.
He confirmed for me that all the Toyota Siennas up to and including 2007 have
no difference in the engine configuration if ordered from the factory with or without the "tow package". He confirmed that the "tow package" for these models consisted only of the Class I hitch. That's it. There's no separate engine configuration, no additional cooling available from the factory. It's one configuration.
Now, as to whether or not their towing configuration is sufficient, that's a completely different discussion. But, you can't get more put onto an engine in those years from the factory.
This all changed in the 2008 model -- they omitted the oil cooler in 2008 and 2009 models, unless you added the tow package. But for 2007 and previous, there is only one engine configuration, and it's designed for towing within the listed limits of the vehicle.
((Another note mentioned elsewhere, is that the Toyota tow rating allows for cargo and passengers within the van itself, which is a departure from many other manufacturers.))
I was very concerned about this very subject, since my van is currently still a lease, so I spoke with National to find out the answer for myself, not trusting what I read on Siennachat or other boards. Fortunately, what I had read was verified
