1st problem - Synchro's worn, possibly due to towing a trailer, caravan etc for a decent period, OR
oil level not quite right.
Long shot - oil is not viscous (thick) enough. Although wonder why other gears like 1st and 2nd are not doing the same.
2nd problem - I can swap your Duramax for my 5spd (I can even chuck in my 3.0L), the you wont have g/box issues at all. :-)
Reply With Quote