I have an 08 View - 07 Sprinter Chassis. I'm limited to 3500 pounds tow, not due to the engine or tranny, but due to the undersized extension members Winnebago used to get back to the hitch. That was corrected in the 09 View. I tow a Saturn L300 wagon, loaded, at 3500 pounds and have had no problems on any mountain in the Rockies. I do shift manually, use a scanguage to monitor temperature, and accept the speed, and gear, I get to keep the temp under control.
Your only real concern will be the max CGVW limitation. You will go over it well before you are towing 5,000 pounds.
You are giving up at least 500 pounds of capability to use a dolly. My suggestion is to look for a more suitable 4 down tow vehicle.
I personally think the tranny is the weakest link, however on the View/Navion forum there are few complaints posted.