Vio

I recreated an Atlas-ish rocket, but it's a pain in the butt. The delta V readouts for the Booster/Sustainerstages (2 LR89,1 LR105) are not correct, because I drop the LR89 after 2 minutes. So everytime I'm trying to modify the rocket with another upper stage I have to guess and run a couple of simulations to get it to orbit. Is there a way to get the correct readings or do I have to make calculations by hand? TY!