transmission shifts smooth and fine but once truck has been running a while will not shift to second. seems like once it heats up it starts doing that. i was having similar problem several months ago but had sensor, neutral safety switch, and manual shift seal, oil and filter changed and worked great for about two months. oil level is good, oil is clean and still looks new. i don't smell any oil, there are no leaks. what could it the causing this problem? I posted this question earlier and received an answer. however i forgot to include all the parts that have been replaced. the parts are included in the 3rd sentence above. Maybe this will help with the diagnostics. thanks!
My car has 159000 miles. My car has an automatic transmission.
I would check to see if there are electronic shift solenoids in your transmission. Basically, the shift speed is controlled electronically through solenoid operated valves. Heat affects these if they are malfunctioning. For example, resistance increases as temperature rises. Also, you could have loose or intermittent connection to the shift solenoids. If you decide to get this fixed, consider YourMechanic, as a certified technician can diagnose your shifting issue firsthand for an accurate repair.