Th350 shifting up and down repeatedly on hills.

[ELCAM]

All that matters is it is not closed. So theoretically no exhaust restriction.

Problem is when the transmission sees 3 inches of vacuum it thinks you have the throttle wide open and it wants to downshift.

Other things that affect the vacuum would be cam, cam timing and ignition timing. Is all that stock?

 

[GBodyVillain]

Yeah the cam and ignition is all stock. and that makes some sense. To avoid it downshifting a bunch I let off the throttle a bit.

 

[ELCAM]

TBI? Carb? If carb what kind of carb? CCC stuff?

 

[GBodyVillain]

It's a TBI

 

[78Delta88]

It's a TBI

I concur with ELCAM, no way the manifold vacuum should be that low at 2000 rpm. And then with the spaghetti bowl of vacuum lines you describe, once that gets figured out I'm sure you will be on your way to a much happier drive.