Don't mean to butt in here. I have a 600w amp (bridged) in my truck, going to (1) 12" sub. I had the capacitor from my Durango. I put it in anyway. I was told it helps when the bass hits hard from the initial "thump". It takes that surge from the capacitor rather than the battery. Didn't need it, but wanted piece of mind.
A 1000w amp, I think, is way too much for a pickup. 300w-500w is plenty, I stuck with the 600w because I was bumping (2) 12" subs in my D-go. Didn't really have the money to lay out for smaller amp.
As is, my door speakers are powered by aftermarket stereo only. Sub-out on the stereo is going to my amp for the sub.
Upgrade the door speakers, get a smaller amp and a good sub. It will sound awesome.
Mike