Bandpass boxes are not hard to model with the proper software, but beware they are not forgiving at all in terms of construction error, unlike a small sealed box. They are also very stressful on speaker joints, and can be run into distress without notice, as the distortion products are somewhat filtered out.
Simply put the gain would be over a narrow band, and the enclosure would gobble up a lot more real estate, so the return on investment is not as good.
I like ported enclosures, but in most vehicles that's a no-go unless you are willing to give up a large amount of room. Space is finite in most vehicles, and especially in a truck, if you consider hauling passengers part of it's duties.
If you want something to slide in for competition, then that's another story. However, for a DD I would stick to a simple sealed box.
What voltage do you have at the battery terminals when you have the truck running with a moderate load? What size of cable do you have run to the amplifier? What amplifier? Do you have enough signal voltage from the head unit to drive the amplifier to it's full output?
To avoid voltage drop for that amount of power, you need at minimum a 4awg copper or a 2/0 CCAW wire.
Once you check to make sure you are getting the proper amount of voltage at the battery connections on the amp, and the head unit is providing a hot enough signal, it's time to set the gains. You can do this with a test CD, play a 0dbfs 60 hz sinewave. Set the head unit to about 3/4 of it's maximum output, and measure the amplifier output voltage going to the subwoofer with a multimeter. For 1500 watts into 4 ohm, you want to have 77 volts AC @ the speaker terminals.
Chances are you aren't getting close to that with voltage sag, and the like.
I should add "DO NOT PLAY A CONTINUOUS 60 HZ SINE WAVE FOR MORE THAN A FEW SECONDS AT A TIME"
1500 watts is a lot of heat in a region where the coil isn't moving much in the gap. Basically, like a heat gun at full output with no where to dissipate the heat, other than by convection.
