It just wont shift into overdrive. i think it is a bad cylinoid on the trany. but im not an expert.

if its not shifting make sure fluids are full (I'm sure you did) im just saying is your speed sensor on trany pluged in , and your throttle return cable from trany to fuel return hooked up

Depending on the year make and model of this car the first thing i would do is to check the trany oil first and then if its an older car have the shift cable ajustment checked,otherwise if its a newwer car then you may have a converter lockout solenoid problem or speedsensor or bad connection at wire going to trany, good day,

This does sound electrical, it may be a sensor problem in the trany thats shorting or a selonoid that bad and sticking, the only problem is a scan tool will be needed so it can be hooked up and the readings watched as it messes up and then remove the valve body to test them, this sounds like its a bad converter clutch lockup selonoid but without doing tests and checking things its hard to say. the best way to do this is to have a trany shop test it, good day.

Have you checked your fluid level lately????? Also try having the transmission fluid and filter changed.

try servicing the trany and putting in some lucas transmission treatment. sounds like the tcc is sticking and needs some lucas to clean it and lube it up.

either ur torque converter isnt geting fluid or one of the valve bodys in blocked and not gettin fluid through thats what im thinking, or could be ur linkage needs adjustin ya . derrick

The transmission should have a vacuum line going to it. It needs this vacuum to shift into the next gear. Try locating it and connect a vacuum line from the carb to the trans.

Check the trany fluid with car on and hot,,
Trany may be bad. or it could just be a cylinoid

bad electrical conections on trany

i have heard that the ignition switch can be faulty and not let the full voltage thru to the electricaly controlled 4l60e trans.i have the same problem with my 95 1/2 t. i rigged a switched wire from the fuse block via a relay to the proper wire on the trans....ask a trany tech and they will know what im talking about,,,good luck