93 lesabre transmission prob

My buddy has a 93 lesabre and it shifts pretty much when ever it feels like it, It dosent slip or come out of gear or anything. It just dont want to shift at all once and a while at first and now its all the time and we just cant figure it out for nothing. I thought maybe the lock up solinoied went out but come to find out there isnt one which is kidna odd being a od transmission and all. But its buick what more can I say. Just like all other cars I went down the line eliminating problems one after another. I just want to know if there was something that I havent thought off yet other than just tearing it apart and change everything. Can someone please help with this issue im at a loss right now.

It could be the modulator or a bad solenoid in the trans. Rather than speculate, it would be better to have the Trans shop scan and pressure test the Trans. By the way, the 4T60E does have a "lock-up solenoid".

It could be the modulator or a bad solenoid in the trans. Rather than speculate, it would be better to have the Trans shop scan and pressure test the Trans. By the way, the 4T60E does have a "lock-up solenoid".
Boy, you had more patience than I did to respond to that one!!