Here's an easy way to do just what Gmachinz said.
extend the brown wire from the regulator plug to the no.1 terminal on the alternator. You have done this already with the brown/blue junction.
Extend the red wire from the regulator plug to the no. 2 terminal on the alternator. This will give the alternator the ability to sense the downstream voltage drop on the circuit and it can adjust output accordingly.
If you notice the no. 2 wire from the regulator plug connects at the same place as the main junction with the alternator charging wire in the harness, along with the other feed wires in the truck harness. Here is the way it looks after the conversion.
If you anticipate upgrading your system with some higher amperage drawing devices like cooling fans, stereo amp or etc you might consider replacing the charging wire with a 10 gauge or even 8 gauge wire. That's the large 12 gauge wire off the back of the alternator. The 12 gauge would handle the fans alright but much more draw might require a larger gauge.