The vehicle will have a higher rpm at highway speeds, lowering fuel economy. The vehicle could shudder, or jump in and out of overdrive.
Typically, when most vehicles experience symptoms that result in overdrive, the issue lies within the transmission. You should take your vehicle to a certified mechanic to check for any codes. You may need to replace or rebuild your vehicles transmission, and this is not a cheap repair (a new transmission after installation runs about $1800-$2500.
Some years of Crown Vics (and Grand Marquis's) develop a torque convertor "shudder" problem. The symptoms are very much like what you describe. It can often be fixed by doing a full flush of the transmission; a FULL flush; not just changing the transmission fluid and filter. The transmission has a lot of fluid in it that does not drain during a normal transmission service so you need to get a full flush at a shop that has the proper equipment to do it (some better-equipped oil change places can do it if you trust them to do so). If it only exhibits the symptoms when shifting to overdrive (and not when shifting from 1st to 2nd, 2nd to 3rd, etc.) it may be caused by something other than the torque convertor issue described above. There can also be an issue with the overdrive solenoid not engaging as it should and causing a shudder when the car shifts into overdrive. I don't know what years this affects or how hard (or expensive) it is to repair. Just be aware that if this is an "overdrive-only" shudder it may be the solenoid or some other component related to the overdrive system and not the torque convertor problem described above.
not shifting
You will need to provide more information on the problem. Is it an automatic or a standard? If it's an automatic, is it a three speed or four speed overdrive, and what exactly are the symptoms? If it's a standard, in what gear and under what circumstances does the problem occur?
There are a number of symptoms that signify a car needing transmission flush and fluid replenishment. These include transmission grinding, problems switching gears, and slipping gears.
Not enough information. What are the symptoms? No spark, Misfire?
MALARIYA is
Under heavy acceleration the transmission will not quickly downshift.
It is important to know the symptoms of a bad car part. The symptoms of a bad motor or transmission mounts are loss the car part, shaking and lots of noise.
These transmission are rear wheel drive 4 speed automatics, that are all computer controlled. Common reasons for the overdrive light flashing are the external sensors on the vehicle like the throttle position sensor or vehicle speed sensor quite often go bad, causing these symptoms. Always run a scanner first to see if a sensor is causing your problem.
what are the symptoms if my transmission filter is clogged on my 1992 merzades es400
Bad transmissions can have several symptoms. The Tahoe could shake, or not go into gear properly. The vehicle can suffer fuel economy, or have trouble driving at speed due to the transmission slipping.