trans problem ?

[jlhamblin]

sometimes on my '92 svx while driving about 60 mph trans will shift back & forth from what I believe is 3 to 4 gear. maybe convertor clutch lock up if it even has one ?. doesn't do it very often but sure messes up fun drive ! engine goes from 3k rpm to 2200 rpm frequently, trans is supposed to have about 10 k on it, anyone know what to do ? thanks for any help, I drive it 700 to 800 miles per week