trans dosent kickdown to first hot at times

[nulu]

Need some ideas for this problem where to look, at times my 94 wagon with 104 engine dosent kickdown when i floor it, i notice it only when hot, when its cool or warming up it will always kickdown from 2nd to first gear, this is anoying me ,stop light to stop light hot starts in 2nd gear and its slow at times , most of the time its fine, where do i start to look first?