I try and have a full tank of gas, proper tire pressure, and I got plenty of junk in the trunk, like full size spare tire, jack, a box full of cleaing supplies, tools....
I get 2.0 or 1.9 60' times with the stock converter on my 255/50/ZR17 RE730s. No spin, unless the track prep is garbage, and it was pretty bad for the racing I did tonight, but I still ran 2.0xxs. I also have HAL shocks, so that might help, even though I ran 1.99xs with the stock shocks, but that was with very good track prep.
Big secret is weight transfer, so figure out what makes your car do that better and you will have your traction problems solved.