I have about 300 miles on the car since resurrecting it from a 26 year sleep. i was driving around yesterday and out of nowhere the trans went to shift from 2-3rd and there was a long flare but it did go into gear but would not go to 4th all the way up until 55 mph. It did this twice then i turned around and went strait home on back roads because i didn't was to possibly do any damage.

Up until this point it was shifting smooth and constant.

This trans is one of the fully mechanical units no vacuum line's and just a bowden rod from the throttle linkage and starts in second.

I have found a couple of manuals on line but i'm still not sure where to begin it seems like its something in the valve body since i still have 1st,2nd,3rdish and reverse. The fluid is at the correct level and is red and doesn't smell burnt( only has 300 miles on it)

Things done to the trans
1- full fluid and filter change with DEX III rated Valvoline non-synthetic(would like to go to synthetic later)
2- All fluids on the car where done before any mileage was put on the car.