tranny problems

Hey guys,
97 cutlass 3.1
213000
Im driving home last night and stop at a red light, and to take off ..nothing in fact rolls back tach just rev like im in neutral. I finally pull it down into 1st and it takes off. So I mess with it some and see what its doing. If I put it in 3rd or OD I wont pull, 2nd is better in 1 st its pretty much normal. So I would just pull it down into first let it take off slow and then manually shift into 2nd then 3rd and OD. Now it will kick down ,but not for that long then it will satrt to slip.Reverse is good, no problem. I have never changed to fluid filter. I checked the fluid its full ,little dark. After I get up and running it does ok just cruising but if I slow way down I have to go back to 1 st. It seems like its not getting enough fluid. Can the filter be clogged bad? And as less torque is needed to push it down the road the less fluid flowing is enough,unless I try to kick it down and it can't keep up so it slips? NO problems at all before.
thanks

WEelcome to AF, bad symptoms here, you could change the fluid and filter, best guess here, it's done.