Tranny Wont Shift

[skokie]

Ok heres whats happenning. 68 1/2 ton with a 350 motor and 400 turbo tranny. The tranny will not shift out of 1st. To make it shift you have to take it out of drive put it in 2nd then back into drive and from then it will shift fine from there as long as you dont put it in park again. I have changed the fluid, metal vac lines and the rubber line that comes from the modulator. Is there anything else that I could look at it?

Thanks