Got '93 Colt Vista...Transmission not shifting as should; if electric overdrive is turned on, transmission self-downshifts to low after warming up.

It sounds like when you accelerate it downshifts and acts like it is in neutral, when you let off, it shifts back to coast like it is in drive. I would question shift solenoid first. I know this is what 1-2 shift solenoid can act like if you have no low 1 and starts in low 2 or 2nd. There are two solenoids, 1-2nd and 2-3rd. You can drop pan and change them easy.

This is a normal condition, the nag transmission control module needs to see a certain temperature of the fluid before shifting into overdrive this is due to fluid viscosity, if the fluid is too thick
due to cold temps the pump cannot supply enough pressure to fully engage
the overdrive clutch, if it did you would have slippage in overdrive

Certified chrysler technician

The short answer, yes. M46 models with the type J or P overdrive (depending on year and market) require a certain level of oil in the overdrive. Additionally, the overdrive is a lot like a standard automatic transmission with one gear range in theory of operation. Therefore, the hydraulic properties of said transmission do come into play here, line pressure, shifting pressure, accumulator and piston function all work together to engage or disengage the unit. Always ensure the unit is disengaged before downshifting and of course, shifting into low reverse.

Do you mean upshifting starts way early? Going from 2nd to 3rd in other words?
Ireally don't know your transmission,but the alternator problem might've possibly spiked and hurt your shifting solenoids in the ******. don-ohio (:^)

it may be a bad transmission modulator valve located on the side of your transmission,vacum operated. a sudden downshift or forward shift when unexpected is sign of a bad modulator valve or a vacum leak to the transmission.best to shop around for a garage w/references when it comes to transmission work though. check all the vacum lines to your transmision,you need to look on the underneath side of your truck on the side of transmission for a loose or disconnected vacum line on the side of the transmission. when you feel the vacum line,follow it to the top of engine,the vacum line is about 3/8th line,and may be disconnected or losing air. to make this short,when you drive the car,start out in low gear and shift the transmission,manually from 1st to 2nd to 3rd does it do right with no slipping? if it does this right and shifts great manually,the modulator valve on the side of the transmissions bad,or a bad vacum leak in-between.thank you for choosing fixya.com

sounds like the downshift cable is out of adjustment, or stretched out. the downshift cable goes to the transmission. CARL,

Not without a little adapting. The 1993 has a 4l60e which is electronically controlled and has shift solenoids. If the 83 is an overdrive it is a 700r4 which is the same trans but not electronic. If you put it in the speedo wont work and you will need to install a T.V. cable so the transmission will shift. The 93 won't go forward or backwards?

well the low cost way to go first would be to try and change the trans fluids. If the problems still remains the it may be an internal problem

You are going to need the transmission rebuilt.

you may have damaged the overdrive gear, a local transmission shop would be your best bet. for good troubleshoting and estimate.