i don't think your rear spring rate is far off. its probably the 12bolt control arm locations putting your IC out in guam.... i don't know where moser locates the uca on their g body castings so you'd need to plot the control arm points. with that much power the lift bars may just produce the hook and spin condition. i went thru that with my car. look around baselines webpage, lots of good info there. if you want i'll email you a sheet to record the numbers and i'd plot it for you. i'd like to see were that 12bolt puts the IC.