1987 chevy truck

[cartersdad]

i have a 1987 chevy r-10 truck with 5.7L and a turbo 350 tranny. from a dead stop as the truch reaches 3000-05000 rpm`s it boggs down and wont shift into 2nd gear unless i back out of the gas. has anyone ran into this problem or what it could be ?

[jeremie]

probably a vacuum line on the intake manifold going down to the vacuum modulator on the trans. My 83 used to do the same thing when the lines broke.

[chevyhome]

If you are using the thm 350 the vacuum modulator itself could have a bad internal diaphragm, normally a pretty easy replacement.