Replace shift detent springs...

I don't think them springs are gonna solve yoru problem. You are talking about the 3 on the back under the shifter tower right?

Anyway, they are easy to do. Its just a pain to sometimes squeeze yourself around the driveshaft and the frame.

 

easy enough to do--you have w-9 right--think you can do them from top--just 4 bolts and you can drop the tower--make sure you throw a rag over the hole and you can get the springs--but like les said--not sure it is going to cure it--i drove an old cabover like that--cept it jumped out of the same gear 90 % of the time--so just had to skip that one---truck was getting retired

 

I'm gonna assume you have and airride cab? If so check to make sure the shifter isn't getting hit by the cab or something. Another thing to check would be motor mounts and trans mount/spring.

 

if you can replace that dash valve this will be a piece of cake---when you put the stick back in --just make sure the bottom part is syraight up and down--some times it might take a couple goes to get it in right---and will need a new gasket--and might be a fuel or air line bracketed to the tower bolts--can just get them outta the way with a bungee