1999 Dodge Dakota Late shifts from 2nd to 3rd gear

My automatic transmission is late in shifting from second gear into third. Sometimes it slips and then upshifts abruptly. I've owned this truck since new, and have changed the tranny fluid once, as well as having the clutch bands adjusted. It used to do this up north in really cold weather, but now I'm in Florida, and it's warm.
There is also a kind of whining noise just prior to the shift that goes away once the shift is completed.