I had a problem very similar to yours. I have a feeling that my truck might even weigh
more than yours. I have two JL 10W7s (30 lbs. each), 3 amps, A lot of weight in MDF to fabricate the sub enclosures, amp rack, and the side trim panels for the X-overs. Also there is the weight of an optima yellow top, dynamat, and to top it all off my spare tire!
So yeah you could say I had some serious rear end saggage with the stock SVT suspension.
I did some searching here on CEG, and contacted SoundQSVT, who had a problem like ours and he suggested H&R springs because they lower the front more-so relative to the rear.
With the H&R springs on my car now it handles better than the stock SVT suspension (minus the stereo) and it has a nice lowered, while still being level look.