Regarding heavy-duty clutches, I think my experience may be relevant.
I've been around two different Toyota clutches; a 2WD with a normal clutch and mine with some kind of super-duper clutch. I have a love-hate relationship with mine. I love the heavy-duty clutch in mine because I can remember burning out the clutch on the 2WD with a winter of busting snowdrifts in and out. That was not a good year. I can dish out abuse to my 4WD clutch with way more confidence because it is a heavy-duty unit.
How do I know it's a heavy duty unit? Well, that's the reason I hate it. You rev the engine up to take off from a standstill, and start slowly letting the clutch in. Unless you're really careful, when the pedal is about halfway up the clutch grabs with a jerk and a ka-bang! and the truck shoots forward (on pavement) or spins a tire (on dirt) while the engine lugs down and almost stalls. After nearly 10 months of daily driving this clutch, I've got used to it somewhat, to the point where my love balances out my hate for it. But there's only so much "getting used to" can do.
