I have a '78 with a TH 350. In "D" the shift from 1-2 is sloppy, at best. When I drop it into "2", the shift is more firm - why? I replaced the vacuum modulator, put in a shift kit and now in "D" when the 1-2 shift happens, it shudders. It feels like dumping a worn out clutch in a stick shift! Why is it better in D2 than in drive?!

Did you check the rear transmission support to see if it is broken. If it is broken, you will be able to move the rear of the tranny from side to side with a small pry bar or large screwdriver. I have experienced strange sensations caused by a broken support. If not corrected early enough, it will also cause the rear seal to wear out and begin leaking fluid on your driveway.

Last one I replaced cost me $12.00 plus tax. Pretty easy to change too.