I have a 60 in a 00 Silverado stock tranny other than the pressure is manually boosted from the regulator. My question is why does it shift in to second while still in manual first? It will shift in to second on its own around 30mph. Is this controlled by the pcm or is it a manual override controlled by pressure in the valve body?

 

bump..

 

I coulda swore the owners manual has a little blurb on why is does it.

But every auto I've driven will shift into 2nd gear when held in first if you reach a certain speed/rpm.

 

Im thinking its probably in the valve body. im assuming once the pressure builds it by passes the spring pressure and shifts it