Transmission shift point change... Please help
 

This morning my transmission was delaying the shift from 1 to 2 by 1 or 2,000 rpm. The shift itself is crisp (as always) no slipping. When it's delayed, I would say it's even a harder shift than normal.

All other shifts are normal -- crisp and quick. Just the shift from first to second has been taking place later.

Throttle position switch? Solenoids? I could really use some help on this.

This is a '92 LS-L, with a new trans, as of a few years ago... The fluid looks nice and pink...