Keep hearing about frame twist with 440s

I tack welded 2x2 box frame to rockers, then spanned 2 more 2x2 side to side under the rocker pieces. I then shimmed the jackstands til it was level on all 4 sides. Most concrete will pitch twords a drain or to the door. Mine is cracked and uneven in a few spots. After the USCT frame ties, torque boxes and inner fender supports, if I push the car on the rack to an uneven spot on the floor it stays straight enough that the wheel of the rack will hang in the air. I would say it’s one stiff fish