so add switch to manually lock torque converter?

 

Not sure about that, would engine stall if it stayed locked and vehicle slowed to a stop?

 

I have just spent 24 years driving on the beach in Hawaii. It looks to me that those tires are more than adequate to move your vehicle around the sand. I have driven similar vehicles in flattened street tires just fine. I don't understand what your problems are. Not getting stuck are you? If you want to drive fast, like in a dune buggy, then you have the wrong vehicle all together.
Those tires seem plenty wide enough to get you around, without getting stuck, or overheating, even in dry sand. Driving in sand is always a bit squirly as far as the ride is concerned. Its not the road.

 

you know, I really don't know.. experiment time! lol

 

Yes it will. Done it.