I had a rebuilt 4500 installed in my truck and since then I notice a rumbling noise. It's most noticable in 4th gear while pulling hard below 1500 rpm and goes away as rpm increases, it also does it a little in 3rd. It also rattles when I shut the truck off in nuetral, doesn't rattle if the clutch is pushed in, has a new 13" SBC. I'm using 5 qt. of Amsoil, and it doesn't shift as easy as it should, you sorta have to wait till the rpms come down to get the next gear. No grinding, just hard and slow to shift.

Didn't have these noises in my old trans.

Any ideas what to look for?

 

synchros going out maybe? If it's just a hard shift, it could also be your master/slave cylinders dying, I know mine was really hard to shift when my master went out. I didn't notice any grinding though. just my 2 cents.

 

mine grinds going into 3rd gear sometimes when im having to shift hard and fast. i guess that could be the 3rd gear synchro's goin out? clutch is a stock one, but pretty new. the tranny did have 96k on it when i bout it, but i just didnt have the time to tear it apart when i put it in back in march of last year. from what i hear the 3rd gear synchro's goin out is common in the nv4500?

 

Try the Mopar spec'd oil, Castrol I belive.