cepx111

I bought some new MT slicks ( 31x10.5wx15 ) for the Nova last week which is the same brand and size we were running. The old slicks were pretty well used up and the sixty foot times had been steady going up making it difficult to dial and hard on my lights.
Ran the car last night with the new tires and the sixty foot times didn't really jump back to where we were running before the old ones went south.
I played with the air pressure going up and down with it and finally settled in at 12 psi which I thought was kinda high but the car seemed to hook up best there. Oddly the less air the worse it hooked which really didn't make much sence to me other than that the tire may have been cupping at lower pressures and not getting a full contact patch??
I usually run 10.5 psi but last night that was out of the question, am I doing something wrong here? Or does all this sound about the norm for new slicks this size?
I did my burnouts the same as before, I even tried less and more of a burnout but made none to little difference. I am stumbed as to why these tires are responding the way they are. the slicks are screwed to the rim so I know they are not spinningon the rim.
Any inputs here would be apreciated. What air pressure are ya'll running in a tire this size?
Thx Charles