Your trouble is that the Dirt Devil tires don't swim. I would agree with Mike that the front tires on an Avenger sit low and probably don't do as much as the rear tires, I believe the wrong tires will still hurt performance. You need eight swimming tires to move you at top speed. Don't forget that top speed is quite slow so anything working against the vehicle will really hurt it. I've had 6x6s with non-swimming tires that would actually move the vehicle backwards in water. Not only are the Dirt Devils not helping you swim, they might actually be working against you.
Everybody dies, but not everybody lives.