Rumble from my 1999 Ford Expedition

When my Expo shifts from 2 to 3 and 3 to overdrive more offen than not I get a rumble sound that seems to emulate from the rear end or transmission. It has been going on for some time and someone I know told me to put this junk in the transmission and It will go away, but It keeps coming back. Expo has 191,000 on it but has been making the noise since 100,000 and maybe before.

When was the last time you had the transmission fluid changed? This is one of the symptoms of failing fluid that the bigger ford transmissions give.
Have the pad dropped and the filter screen cleaned, then get all of the fluid changed (using an exchange machine).

It sure seems like torque converter shudder to me. Does it feel like rumble strips? If so, a complete fluid exchange with Mercon V is in order. Be sure to reset the PCM by removing the PCM fuse or negative battery cable for a half hour. USE NOTHING BUT MERCON V. If your transmission has not been serviced every 30K as specified, good luck, you will need it.

“Someone I know told me to put this junk in the transmission.” Well, there’s a stellar recommendation.

Did you put “this junk” in your transmission?

Of course you did, but “it keeps coming back.” "This junk did nothing to help, and may have accelerated the damage. What were you thinking?

Replace the transmission fluid and hope for the best. It’s all you can do.

Yes it does feel like rumble strips on the highway. I will take it in and have the fluid changed. The thing is I pull a 19 ft boat with it and have done for years and it does fine except rumbles