Sorry about the typo, my mind was tired from working i guess I missed it. On a 350, shift firmness could be adjusted more so by adjusting the throttle valve cable. Some modulators such as those in fords could be altered by using longer or shorter modulator pins, if they were screw in type, adding modulator gaskets could alter them. Additives that claim that they can soften hard shifts are actually just causing them to slip. That is why the shift feels softer. For the most part, additives are not good. There is an item called Lube Guard. That is a good product.