Turbo 350 slippage

My 73 c/20 has a problem.It'll shift from 1st to 3rd without going into 2nd,on normal driveing,from stop to say 40mph. You can down shift manually into 2nd from 3rd and you can feel it go in but give it gas and it'll slip out.????But it'll still feel like it's in. :screwy:

Try changing your Modulator Valve. I had a similar poblem, and that's how I fixed mine.

Intermediate one-way clutch has failed :(