rockford amp with kappa perfect

in reference to an old post of mine( https://www.the12volt.com/installbay/forum_posts.asp?tid=20499&PN=6), i am having troubles with the subs, when one sub is on the spl is higher than if i have both subs on. i have a rockford power 1000a2 and kappa perfect 12.1 svc 4ohm. i have tried running each sub to its own channel, i have tried running both subs to one channel in series and in parallel. i have checked the phase of the subs. the only things i can think of that might cause a problem, are the amp because is it getting kinda old, the loc (first time ive had to use one) and the stock head unit. The vehicle is an 2002 altima running the stock system with 4ga power and a 150 anl fuse, i have the subs each in a 1.0 cuft box (kinda small i know) and the amp is mounted on the sub box. i had 8ga speaker wire runnning but have switched to 16ga for ease of movement to check things.

i ran the loc off the rear speakers, but left them pluged in, do i need to unplug them? everything else i am sure i ran right, i have run it twice in the car and checked it each time, im no really a novice at installs, just have never run across this problem in my vehciles. any help greatly appreciated, i hate having all that expensive sh*t in there and not being able to use the fruits of its loom.

(1) run the amp in stereo mode.

(2) r the subs the same age? Is one broken in and the other new?

(3) does the loc have independant gain controls on it (this would explain alot)

(4) with the loc plugged into the amp, unplug one rca at  a time, listen again to the output. Now reverse the leads rca leads r-l and l-r, does the sub that was playing loud now play quiet and the quiet sub now play loud. If so then look at the loc for a problem.

(4) Is the balance on the factory deck set in the center (easy to overlook).

(5) If there a chance that one sub is an 8 ohm driver? Did you meter the subs (they must be disconnected from the amp to do this).

(6) Can you get a friends subs (any two 4 ohm drivers) and hook them up in stereo to the amp. If the same situation applies, one sub is lower output than the other, then again look at the loc or maybe, just maybe you have a bad channel in the amp

(7) Does the amp have indipendant gain controls?

there is like a two week difference of when i started to play the subs but then out of the box the newer one sounded better. i have run both subs seperatly for about the same time, i have check  the balance of the h/u. i have checked the gains on the loc ( are seperate but set equal) the gains for the amp are also seperate but set equal. i have switched the rca's on the loc and the amp (not at the same time) the sub does not come in 8ohm and i dont currently have the money own a multimeter, but it seems to me that most likely i need to check the amp and if its not the amp need to send the subs back and return for new.

any other suggestions?