th350 won't shift out of first
 

The other day I finally finish up the LSx swap in my Thirdgen and I go to drive it. The only problem is the trans won't shift out of first. It won't shift manually or in the Drive position. I have a Megashifter and I'm pretty sure the cable is adjusted properly. I put 11 quarts of fluid in the trans (I have a deep trans pan). I'm not sure why it won't shift out of first gear. Could it be the shifter cable? Low trans fluid? Bad transmission? Vacuum modulator? Governor?

First check the modulator & see if you are getting vacum.Check line for cracks if that is good pull governor see if the gear is good & see if the valve is stuck.Is the trans used or rebuilt?

It was supposedly rebuilt with a kit from Probuilt Automatics which includes a TransGo shift kit. I just put a new vacuum line on the modulator so that's good. It has an adjustable modulator. Could it be adjusted too high?

I traded a SBC roots supercharger for it. The guy I traded with owns a speed shop and built it to my specs for me. He's a nice guy, always responds to emails and calls and is generally helpful. I don't think he's trying to pull anything over on me. I'm thinking something isn't adjusted right, whether it be the vacuum modulator or the shift cable.

I will check the line for vacuum at the trans. I know it's connected to manifold vacuum because I connected the vacuum line to a nipple on the intake manifold. I'll adjust the modulator and see what that does. I got a new shifter cable and I'll install that and readjust the linkage. As a last resort I'll check out the governor. Hopefully I'm just not getting vacuum down to the modulator or it needs to be adjusted.

I installed the new shift cable today and checked out the governor and the modulator. Both the governor and the modulator are fine, and I'm getting vacuum at the modulator. I haven't had a chance to drive it yet. I'll probably do that tomorrow after work. We'll see what happens!