I've-got-a-87-f250-4x4-with-351W-and-a-C-6.It-has-sat-around-since-2001-when-the-oil-pump-went-bad-we-took-the-motor-out-and-fixed-it-And-got-it-runing-the-other-day-and-took-it-for-a-short-trip.When-we-pulled-out-on-the-road-it-would'nt-shift-into-second-gear-(it-was-in-drive)-so-my-brother-shifted-it-into-second-gear-manually-when-it-got-to-30mph-or-so-where-we-thought-it-would-shift-into-3rd-it-stayed-in-2nd!-Does-the-vaccum-modulator-"thing"-need-replaced-or-does-it-need-rebuilt.It-doesn't-slip-and-is-full-of-fluid-the-flex-plate-and-tourqe-coverter-are-tight.----Sorry-about-my-typing-my-computer-needs-a-new-keyoard.----Thanks-for-your-time-and-listening-to-my-prolem.

 

P.S.-reverse-is-fine.

 

I would start by replacing the modulator, also check and make sure the kickdown linkage is in tact and not stuck in the "wide open throttle" position, as this will make the transmission shift from 1st to 2nd at about 30 miles and hour and from 2nd to 3rd at about 65