I know very little about transmissions so I'm looking for advise.
Trans hangs in second a little long and then during the up-shift from 2nd to 3rd is the real problem. It goes to third and then slips out for a second, revs up and then goes into 3rd. It does it 90% of the time.
any ideas?

 

Yup. But first. Vehicle, year, engine. What has been done?

 

It's a 1989 F250 with a 460 and the C6 is from a 1979 Bronco (truck originally had a C6 in it). The engine and trans are both stock. It has a rebuilt torque converter and I changed the vacuum modulator (was black stripe, now is a green stripe)
I also changed the kick-down from the 70's style to the 80's style.

 

and that would be...

 

"Yup. But first. Vehicle, year, engine. What has been done?"

Was my initial question.

Try adjusting the band but by the sound of it the direct clutches are toast.