I'll be the naysayer here. Changing ratios for better performance while towing is one thing. Towing beyond the ratings is another. I'd consider my liability here.
The Tech 2 will not reprogram for this anymore, as an example see here
http://forums.trailvoy.com/archive/index.php/t-50418.html
Not only will the speedo be off, but the trans shifts will also be impacted as they are partly MPH dependant. A programmer will be required, and in the event of a powertrain failure may complicate warranty claims (meaning customer pays).
In the same situation I would carefully evaluate the financial implications of getting the right truck. If I was towing under or at the rating, there would be less on the table, and I might go for it despite the warranty implications.
