Having an issue with 94 Chevy 1500 4x4. Ran the codes can came up with 66. Replaced the 1-2 solenoid and the 3-4 solenoid. Still won‘t shift out of 2nd gear.
This could be a number of things, dirty filter in transmission, or modulator valve inside transmission bad, bands could be loose inside transmission. Suggest a oil and filter change inside transmission then try it, if no luck change the modulator out, it's inside the transmission, this will need to be done at a transmission shop if you are not mech. inclined. One last not, make sure your wiring to the solonoids are good and also no vacuum leaks if therre is any.
