th350 longtail

In the beginning my car sputtered when it tried to engage in third but not knowing it was fuel related, i took it to a mechanic who then changed my vacuum modulator and adjusted my quickdown and now my trans stalls sometimes and wont go into 2nd gear and the motor will just rev real high but only does it after a little minute of driving but shifts right in all gears when i first start to drive. It also does it sometimes in 2-3 gear. What could this be? Anyone please help!! Is it a bad modulator? How I know which one to get if I dont know the year of my trans but i think it's late 70's early 80's but not sure.

Check the vacuum line coming from the modulator, if it has trans fluid in the line then the modulator is bad. But from the sound of it, its rebuild time cause a bad modulator shouldn't cause it to do what you said. Vacuum modulator just has a Lil say so when it shifts. If its bad it my shift late or early. mine shifted a tad bit late.

A th350 is relatively cheap to rebuild. I'm getting mine built for 300$.700$ if he gotta take the tranny out himself, but I can take the tranny out myself and take it to him. And that's by a guy who builds them for street/strip.