I have a 74 chevy 1/2 ton 4x4 pickup that I didn't drive much for the last year, it sat all winter, it has a 350 with a 350 turbo. The problem I'm having is that it will not shift out of 1st, I check the trany fluid and it is fine.
My name isXXXXX am assuming that your vehicle has an automatic transmission. Transmission fluid has a tendency to turn to a shellac type substance when it sits for long periods of time. This can gum up the valve body in a transmission and cause the very problem you are having. The first approach I would do is pull the transmission pan and replace the filter and fluid in the pan and then disconnect a transmission cooler line, start the engine and pour about 8 quarts of new fluid through the transmission (with the engine idling), shut it off and level the fluid after hooking the cooler line back up. In other words, get ALL the old fluid out of the transmission and converter. The new fluid is very high detergent and usually will free up any stuck valves, etc. The filter is probably 90% plugged which will not allow the transmission to function properly. There could be other problems, such as a stuck governor, etc. But this is your best shot to bring the transmission back to life. It is a messy operation but if it saves the transmission I think you would agree that it is worth your time and getting a little dirty in the process.
I hope this helps you resolve the issue with your transmission.
Have a Blessed & Productive Day!
Thanks for accepting my advise and answer. You will find with me that I like to complete the diagnosis of the the problem, not just start it. So if you would be so kind as to advise me as to the progress with this problem I will continue to work with you to hopefully completely resolve the issue. What I gave you initially was my First step. But that may or may not resolve the issue and I want to help you resolve the entire issue if possible.