So took my 1970 2wd f250 out for a drive, she sits for weeks sometimes just fyi. Made it down about 5 miles and it seemed as if the transmition was simply slipping out of gear. i went down to the gas station and noticed it was a little low on fluid. I put in some atf and checked the level again with the engine warm and in park. It looked right where it should be, so i drove a few more miles and it started doing it again. Here is the fun part... when i turn the truck off and put it into park, wait a few seconds and turn it back on i can shift it into drive and it goes no problem .. that is for a few miles and then it slipps out of gear again. I can turn it off again put it into park and do it all over again. Thats how i limped home..

so.. any ideas..

thank you for your input ahead of time!

 

That is a classic condition of a filter that is clogging. What happens is when the truck is running the pump in the trans is pulling fluid from the pan, small particles in the fluid eventually find there way into the filter until it chokes off the fluid to the pump and the trans fall out of gear. Turn off the engine and the fluid flows back out of the filter until the engine is started again and the pump in the trans pull fluid back into the filter and it happens all over again.

The big issue is the small particles came from somewhere in the trans and its enough to clog the filter. A rebuild is in your near future.