Noise/vibration in 5th only while accelerating
Running without 5th is fine, but I wouldn't go really fast (like highway) without OD. 4th is fine up to about 55 or even 60 MPH, but I honestly wouldn't reccomend going past that. It does sound like OD might be going out.
I reccommend a fluid flush. Drain tranny, put in cheap fluid, drive around about 10 miles, drain tranny again, put in good fluid of choice.
After you drain it the first time, check and clean the magnet on the drain plug.
See if that makes any difference, it probably won't. If it doesn't, a visit to a family tranny shop is in order.




