TH350 short shifting

[Batman]

I did some searching and couldn't find this exact problem with my TH350. So, hopefully there are some good tranny guys here.

If I let the transmission shift on its own it shifts very short, into second at 20mph and 3500RPM, 3rd at the same RPM and 35mph. Not really sure what gears I have, running 33" tires. It doesn't feel like it's slipping at all if I manually shift it I can wind it up and it doesn't seem to complain. I've adjusted the TV cable over and over, the vacuum modulator is in fine shape and adjusted for the highest possible shift (from what I gather this is only good for 2-3mph). I'm pretty close to just having it rebuilt, I don't think its ever had a rebuild. Anyone have an idea, if I can get away with not rebuilding it for a few years I'd like to.