I have a TH-350 that will shift into all of the 3 gears prematurely with a light throttle.. instead of each gear winding up for a bit. So I'm in 3rd gear before I get to 35mph. I suppose it has something to do with the linkage from the trans to the carb?? Any thoughts?

No, probably needs a governor tweak. You need lighter weights to change the shift points.

I had a similiar problem when I bought my car 5 years a go, turned out that the hose for the vacuum modulator had been disconnected. Or maybe you have a broken modulator?

I would start with the modulator. Pick up a new adjustable one, they are cheap. Install it and play with it. It WILL affect your part throttle shifts.

In my experience, if the modulator isn't hooked up it won't shift out of 1st.

Where does it shift at WOT?