Wheel Spin Problems Need Advice

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Hey guys been up to the drags twice recently and i'm pretty disappointed
i have a n/a fg xr6 5 speed auto, now its usually running constant 14.1 - 14.3
with a average of 2.1 60ft.

I have changed my rear springs out for very low springs and changed my tires (from ATR Sport 2's to Nitto invo's) (245/35R19)

now when i ran a few days ago i was running high 14's to low 15's, i cant seem to launch i just keep wheel spinning, i have an open diff witch doesn't help but with my old tires / springs i could almost launch as hard as i wanted recently i have gone from 2.1 60' to 2.5 60' cant seem to get traction?

the tires i have changed to are apparently "high performance" tires at almost $300 each i would expect them to have at least some grip. (Nitto Invo's)

Weather i just take off fast or launch at even 2k rpm they will just spin (even on the street taking off quick they wont grip)

could this be a cause of bad tires or my rear springs? The springs have almost no movement in them (i always thought that springs can make a big difference on how a car puts power to the ground, hence drag racing suspension you can buy.) could no movement in the rear springs be causing me to spin?

I have tried the car at 40psi all the way to 30 psi, cant really go lower as i have to inflate / deflate at the servo as i don't have a pump and don't want to drive on the road with below 30 psi.

Cheers guys, any help is very appreciated