2001 Sebring hard downshift at 25mph
 

Only does it right at the 25 mark. Up shift and other gears work smoothly. Only when stopping or braking. Was very low on fluid, topped off with fluid and Lucas additive. Took in for a diagnostic, was told there is a small leak under tranny? where cooler line is. Wanted a couple of hundred dollars for it. Do you think the small leak could somehow affect the whole car and shifting? Should I drain the fluid, seal it, and change fluid and filter first? The diagnostic threw about 6 codes, something about speed sensors or solenoids. Could it be related to low fluid? Has anyone been through this? Please help.

Low fluid could cause weird shifting.
These tranmissions are notorious for leaking at the solenoid pack. If you browse around the forum and look for posts regarding the solenoid pack, you'll find some information including how to replace it.
If you have someone who'll replace the solenoid pack for $200, that's not too bad a price, though you can do it yourself for under a hundred if you're a little handy and have some basic tools.
It's probably a good idea to replace he cooler lines while you're at it, as you are right there, the part cost is low and they probably need it.
Given the age of the car, it's probably due for a fluid change (not just a top-up).
Speed sensors are also easy to change and not terribly expensive and you actually have to pull one of them to remove the solenoid pack, so if yours are bad, consider replacing them.
Hopefully there's no internal damage.

hard downshift at 45 kph
 

I'm having the same problem. If it gets into 4th then downshifts around 45 k/m (28mph), I get a hard jolt. I also had low fluid, but the downshift problem wasn't very noticable until after I topped up.
Just had it at the tranny shop this morning and tests show pressure is 92psi when the max should only be 70. They say a snap ring of about 6-8" diameter may have broke, or other wear and needs a tranny removal and internal inspection for about $1500-$2000.
Please post your findings,
Thanks, Ron

Forgot to mention. I had tranny problems about 6 months ago where it would'nt shift out of 1st (Limp mode) and getting a couple OBDC's. Tried reseating connections, checked grounds etc., and ended up replacing the Tranny Control Module ($65 from a wrecker) with one that had the exact same code # but didn't have it calibrated since it seemed to work just fine.

Fixed itself
 

Phew, thank goodness it was nothing serious. We ended up using the other half of the Lucas additive, topped it off, and drove around for about a week, and that was it. It went away and now the car shifts smoother than ever. I guess it just took a while before the fluid started working properly. I also checked for the leak myself, and it is a very very very slow leak, almost unnoticeable...I probably just need to reseal it with sealant later. I am glad it went back to being better than before and I did not have to pay over $200+ and not have the problem fixed at all.

My hard downshifting problem has gone away. I also added the Lucas additive, but I don't think that really fixed it.... here's my theory. My problem started with the trany cooling lines leaking at the rad. The rubber hoses got hard, and probably shrunk some at the connection and leaked out much of the fluid to a point where it would not shift into gear right away. I repaired the lines and filled the trany to the proper level with the proper fluid. Thats when my hard shifting started. Many people have had the same conditions. Fluid goes low, fill it up, and the hard shifting starts. The TCM (Transmission Control Module) is a "adaptive learning module" which means, it adjusts to drivers driving habits, and engine performance and transmission performance. I think that as the fluid goes low over time, the pressure drops, and the module adusts the solinoid pac fluid flow to compensate. When the fluid is then topped up, the TCM takes time to learn the new higher pressure level and still shifts the trany as if the pressure was low. It took about 2000 km for mine to cure itself completely. I gradually got better during that 2k. Normally when the dealer or trany shop do a repair, they would recalibrate the TCM to default. I tried to have this done, but the dealer was not able to communicate with the TCM, but they could talk to the BCM (Body Control Module). I found there are seperate wires going to the OBDII diagnostic connector from the TCM, so maybe the dealers OBDIII was not switching to those wires. One poster suggested shifting into neutral as you are slowing down to the point where it downshifts hard, which is what I did to avoid the strain on the trany. The Trany shop I went to showed me the gear housing which often breaks because of the hard shifting and if that breaks it means a teardown. My guess is if you have a loss large loss of fluid, repair the leak and then ONLY add a cup or so every few days, and you may not see the hard shifting problem.