Hi Philip,
I will try to take a stab at this. Knowing that you don't tow a whole lot or rarely move anything greater than 7K, I think that you might be better off with a 12 cm wastegated housing. You can probably get one real cheap from a 2nd gen. I think it would help the with the take off in your truck, especially with those really tall rear axle ratios. I kept the 16 cm housing because I will be towing a lot and need as much air flow as I can get. Hope that provokes a thought or two.
Jeremy