If it's only when you attempt third gear the problem is in your transmission.
it can slip
the synchronize in the transmission is bad, that why the jumping out of fifth gear
they dont slip even if they have broken teeth
Mid Slip, Silly Mid slip and third man sound like cricket positions you may be confused as there is a mid on or mid wicket and a silly mid on or silly mid wicket but not a silly or mid slip.
automatic: the band or bands controlling the activation of gear are worn OR the friction plates are worn manual: the gear teeth are worn or out of allignment
No. Heat it with a plumber's torch and it will slip right on.
Quite possibly a worn second gear clutch pack.
Because your transmission is burning out. I have this exact same truck and the OD started to slip about 6 months before it and third gear finally went out completely. As it was slipping it had a bad tendency to "search" for a gear while cruising at 70 mph down the highway, and would constantly go back and forth and would slip into OD when it went. The tranny did have 160,000 miles on it, so I didnt complain when I had it totally rebuilt for $2,000.
Death is the third from of slip
Worn out gears in a transmission will cause the transmission to slip out of gear. The gear may be war only on one side, causing the transmission to work properly. At times.
Transmission temp sensor can cause a slip or high rpm before shifting to next gear.