Manual 3 on the Tree - Hard to Shift

[javelinmania]

I find that I will get stuck in one gear and can't change gears. I especially noticed it when in third gear - but it could be more. I've only had the truck for a few months and in that time have only had it on the road 3 times as I work thru the issues. What little history I know that there has been at least 2 engine changes and countless other changes. What would account for not being able to get it out of one gear and into another? Steering Column, Steering Column to transmission linkage or transmission? I'm guessing the first two. Sorry, but I can't at this point tell you which manual transmission is in the truck - they all look the same to me. It started life as a V8 truck and it now has a 78 350 in it. I'm assuming the transmission is original.