Describe Firm Shifting from Soft Shifting.

Hey I have a 1975 Ranchero with a 400 and a C6

My transmission, is shifting late....... around 30 and 50

just re-placed the transmission modulator cause it was a little bit faulty...

i need to shift at 20-25 for fir shift and 30-40 like it use to

what do i need to adjust to make my transmission shift at these proper times..

i put it in my friends shop and my shifting has never been right again since then....

I think he was Mashing down on my stuff and F*d it up...

it has 3 gears....

Do i just adjust the modulator?