Chrysler Repair: PT Cruiser trans: harsh downshifts, routine maintainance, mileage range

Question
Last week I had my local mechanic change and replenish all fluids (oil, trans fluid) also a lube . My 2002 Cruiser has 168,000 miles.

After I picked up my car I notice when I put on brakes to stop and the car downshifts, right at about 25/20 mph there is a jerk or shudder. This wasn't happening prior to the routine maintainance. I went back to the guy the next day and he said some Cruisers don't react well when the trans fluid has been flushed and refilled. He drove the car, added a fluid that he said was an additive to help.

The car is still reacting the same. It's been 3 days.

Any ideas?

Answer
Hi Diane,
Does the work order/service receipt say what type of fluid was used to flush/refill the trans fluid, and how much was used? And what was the additive?
I ask because Chrysler trans's have long-standing requirement that only type "ATF+4" fluid be used in it. Nothing else, no special additives. Problems otherwise are likely. So my advice would be that all the fluid/additive in the trans be power flushed out (that is a total of 8.6 quarts if the removal is totally effective) and then only ATF+4 be used to re-fill it. Draining the fluid only removes about half of the fluid, so that is not adequate to get rid of the contaminant that is in there now. Then see how it shifts.
Harsh downshifts (even with only ATF+4) can be due to a variety of causes; but the only simple non-mechanical/hydraulic reasons are: low fluid level/consequent aeration of the fluid or idle speed too high. But improper fluid could also cause this behavior.  
I would hope this will correct the situation, but you are in the mileage range where these transmissions often need a rebuild. However, the trans control computer has a self-diagnostic capability which you can access with a code reader that plugs into a socket under the dash next to the steering column. Those codes are the most direct way to decide if a rebuild is needed.
An Autozone parts store will likely do a fault code readout for free, or an independent shop will do for under $40. Ask the local mechanic who did the maintenance to do it for free, possibly, if you trust that he has the power flush unit to clean out the trans and will reliably use only ATF+4 in the refill. If not, then go elsewhere for a readout. Ask for the 4-digit fault codes, what their name is, what it means, what is recommended, and for how much. Then before you do anything, write back and we'll compare that to the Chrysler trans manual.
Roland