Swapped to 528 mech cam slowed down

Yes as far as tuning its good. Engine will rpm in the 1/4mile to 6200 no problem. This engine is a 030 over 340. stock x heads stock 71 TQ setup,3500 stall, 4.56 gears. this setup was a consistant 12.5 car before with the comp cams 305 magnum cam. My 60 foots were only 1.8s But that was with worn 340 springs and stiff shocks. Now I have lost traction. and sixty in the 2.0 and worse. I realize that the rear needs attention for better sixtys. I am probably going to throw
on the ss springs. Didnt want to but dont have a choice.