Seems like there's a few different questions in this post...

1) managing larger tires with the 3.7L
Not really much you can do there until gears become available IMO. Most of the "power" mods on the market squeak out a small performance gain at the peak levels... this doesn't often translate in actual power gains since the gain % diminishes as the RPM's lower and it's minimal in the RPM range that you normally drive at (ie: 10hp increase at peak 5000RPM may only be 1.5hp increase at 2500RPM)

2) the effect of larger/heavier tires on the suspension system
Inertia is the issue with unsprung mass. A simple way to think of it is when the tire hits a bump in the road it must move upward, it's motion must then stop and move back downwards- changing directions of a heavy object is much more difficult than a light object... think of a soccer ball; someone rolls a soccer ball to you and you kick it, no problem... but what if someone rolls a bolling ball at you and you try to kick it? >>>> well the bowling ball is the heavier tires and the shock/spring is your foot. The offroad oriented suspension systems are better at handling the unsprung weight, but also firms up the ride in the cab.

3) trade off between unsprung weight from tires and ride quality
The best thing you can do to account for the unsprung weight of the tires for both ride quality and efficiency is to find your optimal tire pressure. Too much pressure increases the effects of the "bowling ball" since the tire must react to almost every road imperfection (hence why everyone complains about E-rated tires because they don't realize that the pressure stamped on the sidewall is waaaaay too much for their application). Too low of a pressure however will reduce MPG and may also overheat the tire. So there's a balancing act there.

Hope that helps some