My cadillac has slow pick up I just had the trasmission changed and I have to put it in 3rd to drive it

I wouldnt bank on this but it sounds like a shift syliniod

You are having an ELECTRICAL or SOLENOID problem... Since Manually you are able to get the gears to work properly, then I would be looking at the Electronics and / or the Shift Solenoids (Solenoids FIRST).

There are items called "shoes" or the plates that shift vehicles. Reverse and first are commonly used to gether in most vehicle. The trasmission shifting shoes need diagnosed.

Since the transmission in this car is electronically controlled the first thing that must be done is to have the transmission control module scanned for fault codes, that is numero uno.

Looks like the transmission does not see the speed, check speed sensor and transmission fluid level while running.

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Did you change the filter and the 5 qts of fluid or have the whole system purged with 13 qts and no filter? Did you use the right fluid? Did you check the fluid after driving the car a few miles? How was it running before the change? It is possibly coincidence that the tranny is not shifting, The fluid change would not cause that unless you didn't put in enough fluid or you put in the wrong stuff. The first sign of low fluid is not shifting, check it out, hope this helps.

this is one of the first "fuzzy logic" boxes fitted by honda,
the gearchange pattern will change dependant on the driving style of the driver.
first check the trans level.then without touching the gas put car in gear and let it run to max speed(about 30/35mph).stop.
then put 1/3rd gas pedal down (keep it still)and let car go to max speed,stop.then floor the gas to a safe top speed for the test road...then stop.you have just reset the change mode.
if you drive the car with only 1/3rd gas the car will change lowdown the rev range(boring) and save you a fortune in gas...
if son drives different to you the car will know who is driving and change accordingly(takes about 30 miles to react)
it is NOT in any handbook.

might be clogged catalytic converter it can cause loss of power due to carbon built up that's why it seems like it takes a bit to pick up speed

the trasmission fluid leval may be low or your cluches are slipping. check the trasmission fluid leval with the engan wormed up and the trasmition in park pull the dip stike with yellow on it and check the level alsow smell the dip stick if it smells burnt the the tran fluid need to be changed.
if it is low put tranmition fluid in it by using a long funal and put the fluid in the tranmition dip stike tube. If the leval is full and the fulid is not burnt it might be trasnmiton cluches and the tranmition needs to be rebilt.

is it when the car is in 3rd gear automatique trasmission and change to lock up mode if its what you call that its lock up selenoid its on the driver side of trasmission on the side cover its call lock up switch too please dont forget to rate this if its a fixya its better for me thank you advance