It's high miles (220,000), but otherwise has been doing quite well. The other day on the way home on the highway (pulling a trailer) all of a sudden the rpms's would shoot up to 3500 or better. So, I instinctively let off the gas. The rpm's came back down. A couple seconds later I got back on the throttle and everything re-engaged normally with normal torque. Then after a few more miles, it happened again. This happened 3-4 times before I stopped at a restaurant, and let it sit for 45 minutes or so to let everything cool off. Btw, these symptoms occurred whether I had over drive on or off.

I checked tranny fluid. Level was a good 2 inches above full line. Don't know if that makes any difference. I think it's been full like that for quite awhile with no issues/symptoms.

After letting is sit those 45 minutes, I got back on the road. After another 8 miles or so, same thing happened again. Then I drove the last 30 or so miles with no issues till I got home. I haven't driven it since that trip.

My first reaction is that bands are slipping, which indicate a need for rebuild/replacement. But, since this is an electronically controlled tranny, is there a sensor that I should check that could cause this? The check engine light has not been on in a long time. It's been a good truck for me overall.

I haven't verified 100% that the transmission basically slipped (disengaged), causing the rpm's to shoot up, as opposed to perhaps the trasmission downshifting and bringing the rpms up. But, it sure felt like it was slipping and not downshifting. Next time it happens I should keep on the throttle instead of letting off to verify that.

Any ideas?

 

This is just me but I would start with a tranny fluid flush and new filter to start. Sometimes the simplest solutions are the best fixes. That said if your tranny is original with that many miles I would consider a rebuild but do the simple fixes first..... I don't know much about the electronic trannys. Mine has a C6 which has its pros and cons but it was slipping a bit. New fluid, filter, and new deeper pan with a fluid drain plug and she was running fine again.

Of course this C6 on mine only has 98K currently. I don't think its bad to have a little over full mark (2 inches seems like a lot) but then again it does put slightly more pressure on the seals and changes the amount of time to get the tranny to an ideal viscosity/ fluid temperature. Of course the #1 killer of a tranny is heat so I would rather it run too cool then too hot. Kind of like I would rather overpower a subwoofer then under power. Someone else might beg to differ.

 

Just like the E4OD, the 4R70W is also 100% electronic controlled. Check for codes.

I would also HIGHLY suggest you draw off some fluid to bring the level back into spec. Never ignore the obvious, fix what you know is wrong first

 

Right, I will draw some fluid off.

The fluid is fresh, clean, and does not have a burnt smell whatsoever. The filter has been changed within the last year or so when I did a complete flush/fill.

I suppose there could be a code without the CEL being on, right?

There was a bad leak somewhere in the system (that has mostly cured itself, btw) that precipitated me adding tranny fluid fairly often. That's why the fluid is quite fresh, and that's also why it's overfilled. I wasn't being cautious enough when filling.

 

There still can be codes stored and no CEL. Innova makes a good cheap reader which is on amazon for $25, cable is a rip off at $25 as well but worth it if your a one man diagnostic team. Comes with the booklet of all codes.

 

Thanks for the tip on the code reader. My brother has one, so I should be able to do that tomorrow.

 

Put the truck on the scanner. No codes, except for 225 (knock sensor).

I pulled a bunch of tranny fluid out and put in Lucas tranny fix. Fluid is now at the proper level. See what happens. I plan to take it out at least 100 miles this week pulling a trailer, so that will be a good test.