2001 GC transmission

When slowing to a stop, the tranny seems to be jumping from 2nd to low too quick. It feels like the front brakes are locking up for a brief moment. (no the front brakes aren't being applied at that moment) After all is warmed up, the problem goes away. Suggestions? I'll get back to you all on the fluid level. I know it's due for a fluid change. 78,000 on the tranny.
No problems shifting up and acceleration feels normal. I did the key-on key-off 3 times and the trip odometer said "done" with no error codes in between.
Any thoughts?

Sorry 3.3

Hi, Here's a thought...It's about time you thought about the fluid change, The specefied mileage in the owners manual is fo under IDEAL conditions,,Average fluid change should be 30,000 miles...Your welcome, Clay.

Fluid change is definately on my list. It was changed at 25000 when I first bought it. Thanks!