Th-350 shifting

[kaycee]

Hey I got a TH-350 with a B&M shift kit 2K stall it shifts real early from 1st to 2nd like around 1200RPM'S then it seems to hold in 2nd for a long time before it hit's second.This happens when I mash the gas ,it performs good when driving normal except it still shifts to early this has done it since I first got the trans.I have allso tried to adjust the vacum modulator but seems there is no improvement or change new modulator was installed and still no effect.Now I have turned the screw like a bazillon times each way in/out.How can I find out where this needs to be so I can start from scratch?What is causing the shifting problem? Thanks for the info