My opinion on Timbrens is fairly well known...they're a scam.
I had them on 2 '05s and the frames broke right behind the front axle. Not being an engineer or physics major I figured this much out. Basically they are just a replacement bump stop but taller than OEM. So when you bottom out on that bump stop, despite being made of rubber, that energy is transmitted somewhere...which is to the frame. The weakest point in the frame will fail eventually because of that energy being transmitted to that point.
So if it were me, I'd throw the Timbrens away, reinstall factory bump stops and buy airbags. Or those variable rate coil springs.
We tried heavier springs on my RAM 2500 (wonder what towing capacity it has) and it made the truck just about undriveable when the plow was off. Ended up with airbags and it rides fairly nice and carries the weight far better.