Double-clutching is a sign of worn synchronizers. Replacements are available from the usual vendors. Any lube other than 90wt pure mineral oil will, in time, ruin brass synchronizers.
Jumping out of 3rd is usually a worn shifter fork in conjunction with a worn input shaft and bearing.
Get one of these publications on overhauling a torque tube 3sp. Find one online.
Attachments
20240107_111457.jpg (344.75 KB, 150 downloads)

~~ Jethro
1954 3100
Back to Life
In the Dity Gallery
1951 3100 (gone) / 1956 4400 (still in the neighborhood) / 1957 6400 with dump body (retired) / 1959 3100 panel (in the woods junked) / 1978 Custom Deluxe K10 / 1993 S-10 4.3 / 2004 Chevy Crew Cab / 1945 John Deere H / 1952 John Deere B / 1966 John Deere 2510 / 1967 John Deere 1020