Th350 Wont Shift

I have a th350 out of a 1972 chevelle. I just rebuilt the small block 350 and had the th350 rebuilt. The transmission will shift into reverse and drive(1st) great, but will not shift into 2nd (or any other gear for that matter). The transmission has a new filter and new fluid. I made sure my vacuum line is hooked up to the modulator in the rear. I am running a cam that gets 10-12 lbs of vacuum at idle, is that maybe not enough vacuum? I am stumped. Any and all advice would be great. Thanks!!

I have a th350 out of a 1972 chevelle. I just rebuilt the small block 350 and had the th350 rebuilt. The transmission will shift into reverse and drive(1st) great, but will not shift into 2nd (or any other gear for that matter). The transmission has a new filter and new fluid. I made sure my vacuum line is hooked up to the modulator in the rear. I am running a cam that gets 10-12 lbs of vacuum at idle, is that maybe not enough vacuum? I am stumped. Any and all advice would be great. Thanks!!
Im running 15 hg's of vac right now and my trans shifts fine! Not sure if your vac being so low is a problem but its something id take into consideration!

Even with little or no vacuum, the trans should shift into higher gears, even if its at high revs.

Did the trans ever shift properly after the rebuild?

My Haynes GM automatic transmission service manual lists the following explanations for your problem.
1. Check the governor assembly for sticking governor valve.
Governor drive gear worn, damaged or retainer pin missing.
Governor weights or springs missing or damaged.
Exhaust check balls missing or damaged.

2. Check valve body for :
sticking 1-2 shift valve.
Spacer plate or gaskets incorrectly installed or damaged.

3. Check the case for:
valve body face warped or damaged.
governor filter plugged or damaged.

The manual also suggests to look for plugged fluid passages, damaged clutch piston seals /bores.