Dave has pointed you in the right direction in Australia. I haven't done it, but I've contemplated it.
Personally I don't tow in 4th, I leave it in overdrive and allow the TCC to lock. The lower stall speed TC would help me, but I've got other things to spend my $ on at the moment. If my TC failed I'd be on to them in a flash!
We're now towing 2.5T (we towed our 1.8T van that you see in my current sig for around 50,000km or so) but I've only got part of two different tanks of fuel under its belt, so it's hard to gauge economy figures. It's looking a little like 19LPHK staying at the speed limit, and around 15LPHK if I sit on 85 km/h, but we've got a trip at Easter that should use most of a tankful so we'll be able to get a much better idea of consumption then.
Wholesale Automatics will probably try to sell you their new valve body as well. It might be worth it - particularly if they can give you a switch that locks the TCC whenever you want it. You'll have to ask - they produce a TCC override for other brands, but they ignored my email query about a TCC lock for the D40.
