Abrupt slowdown at speed...thought it was cruise, but....

[DeckArtist]

So last month I have my 1250 pound trailer in tow on the way to pick up wood in Dallas. Tow/Haul mode with MDS deactivated via trans in D8 mode. Traveling 70 in the HOV lane. Hit a bump in the road and the cruise shuts off with what felt like a huge downshift. Gear was in D-8 and now is in D-6. Sacred the S outta me, but I made it to the lumberyard without any more issues. Decided not to run cruise on the way back home [55 minute drive].

Didn't use cruise for a few days thinking that if it was the transmission it would repeat the problem. Made the second trip back to Dallas with the wood on the trailer without incident [not using cruise still].

Last week I was driving without a big load all week using cruise with no issues. Today going into town had cruise set on 74 mph and the same thing happened [not in tow haul mode, trans in D-8].

Pretty sure it's the cruise control, but would like to know if anyone else has had this issue and what was the fix?

 

[DeckArtist]

Almost forgot...made several 200 mile trips in between the two incidents using cruise control without a problem. Today's abrupt downshift and cruise shut off happened without hitting much of a dip in the road.

 

[JohnnyMac]

My 14 2500 would kick out of CC quite often on bumps. I think the type of bump and if it detects any slip or wheel spin makes a difference. I traveled roads back and forth to Valdez, Alaska and the roads had pretty significant frost heaves. I don't recall it ever downshifting though. Do you have trailer brakes? Could the bump have engaged the trailer brakes somehow and they pulled the truck abruptly which caused the Anti-Lock or Traction Control to momentarily engage as either of those will disable CC? I'm just thinking out loud here a little.

 

[crash68]

If the trailer has brakes, the truck ITBM has Trailer Sway control(or the truck's ESC) that may be causing the issue while towing.
Does the trailer seem to wander behind the truck? Maybe the trailer axle isn't straight or you have a wheel bearing going bad and the truck is sensing what it thinks is a problem.

 

[DeckArtist]

I do have the trailer brake option but today it happened without the cruise on and without the trailer behind me. Trans was still in D-8. Feels like an abrupt downshift, but today it didn't change gears. 75 mph on the freeway at the time it happened. Could be the trans, transfer case or rear end I guess, but no clue which one is causing the problem. Could even be the traction control I suppose. So far there is no common denominator other than freeway travel and speed [75 mph or thereabout]. Didn't happen on the way home.

So that's three times so far...once last month and twice this week.

 

[DeckArtist]

Think I will turn off traction control for the next trip after lunch and see what happens. So far never twice in one day.

And no trailer brakes.