GMC crew cab rear speakers

I'm having a problem w/ the rear speakers in my 02 GMC 1500HD crew cab. The fronts are just fine, but the rears can't seem to keep up. It seems as if there is an attenuator somewhere on the line. Here's what I'm running: deck: Pioneer DEH-P77DH (22wx4 RMS/45wx4 peak) fronts: stock separates rear: Kicker K65 (6 3/4" coaxials, 65w RMS, 130w peak) I just swapped the stock rear speakers with the Kickers hoping to beef up the rear fill, but they're not any louder, just crisper. Also, the stock speakers are 8 ohms, so I assumed that by putting in the 4 ohm Kickers, I should get an increase in sound. Also, there was no significant increase in sound in the stock rear speakers when I switched from the stock deck to the Pioneer. This leads me to assume that there is an attenuator somewhere in the factory speaker wire for the rear speakers. My options are: 1) run new speaker wire from the Pioneer to the rear Kickers to see if there's a difference, 2) the costly alternative ... get an amp to power the rear Kickers.Friends Don't Let Friends Bump Stock.

I agree! That's standard practice with me on those trucks. I have not bothered to search out why the trucks are that way.