tramsmission goes bump bump bump

[omrebel]

It's a 99 with 150,000 mi 4x4-transmission works perfectly EXCEPT when in
overdrive and driving 40-50 mph--then it goes bump,bump, bump like it wants
to shift up to 3rd--if you speed up( & transmission shifts to 3rd) or slow down it stops--just when trying to
maintain a steady speed. (Also when this is happening it -sometimes-won't let you turn overdive off). My mechanic says no codes show up. Any ideas?

[ipz2222]

''Also when this is happening it -sometimes-won't let you turn overdive off). ""

Sounds like the wire from your od switch is rubbing inside the steering column.
Preston

[omrebel]

Thanks for the reply-that will give me a place to start..