Just got my new 13 4runner Limited--who has replaced speakers?

[H&KRunner]

oh my

 

[gago1101]

If I'm picturing correctly you have a gap between the speaker and the door? i.e. you've just used bolt spacers and have left the remaining area open? That is not going to give you very good performance - you want to isolate the back wave as much as possible. That might also explain why you are able to keep your doors from rattling etc, you aren't building any pressure in them at all.

I must be misunderstanding though...

I need spacers I'm running 8" speakers from HAT and they just barely clear on both sides. I am using quality hardwood spacers though that are treated with dynamat material as well.

I am using high quality amplifiers, nothing to be gained in that department.

If you're interested in taking a look at an alternative view on the importance of damping factor in an amplifier have a read:
Damping Factor a Misunderstood Rating

The remaining open gap area is filled / sealed with heavy acoustic foam, such that no soundwaves are escaping. I think this is the part that prevents rattling as well as gives good performance.

Edit: Damping factor
It is misunderstood by some. I have been working for more than 10 years building my home audio. What I have now is a class D Wyred4Sound amp driving my 10 inch woofers (2 in each speaker), while the mids and the highs are driven by separate tube amps. I have tried several pure class A and classA/B amps as well as tubes for driving the low end. There are no match for a high damping factor amp (usually >2000), especially in regards to bass articulation. I am talking about the bass your hear, for example, in night clubs, clean and punchy going right through your chest. Why is their bass so good? it is because they use high damping factor digital amps. If you like soft and boomy bass, than tubes would be the choice. This is the reason most good subs will have digital class D amps. Finally, midrange and treble are a completely different story.