coffeegoat
Adventurer
Oh, and based on this thread I said screw it and ordered 4 new O2 sensors, because if they can improve my gas mileage by 1 MPG, they'll pay for themselves in ~10k miles, and 2 MPG will do it in ~5k miles.
The flush is different than changing the fluid. Flush will always put the same worn fluid back into the transmission. Most shops are against replacing fluid because of the cleaning detergents in some fluids causing more damage. However, changing to new fluid and filter with the correct SP-III fluid should not cause any problems for this transmission. I changed it at 170K on my '01, 110k on my '05 and I will do it again on my '05 when I get a chance.
As the fluid gets old, it loses its friction properties which causes slippage in the clutches and odd torque converter behavior. My 01 had multiple flushes done for what felt like a rumble strip/gravel road as I accelerated under light load up hills and around 40mph once it got to 150k miles. The flush would help for a few months before the symptoms returned, only worse each time. At 170k miles I found someone else describing the same problem and the fluid change procedure. I didn't change the filter that time, but I cycled the engine to pump the fluid through the cooler hose 2qts at a time, shutting the engine off when flow stopped to add more new fluid until it was all the same deep red color. Afterwards, the truck drove like new. No more shaking, rumbling or odd transmission behavior.
I drove my 05 in manual mode in 5th to confirm what you are seeing and they seem to unlock the converter when decelerating in the calibration. When I shift to 4th manually at the same speed, it locks and holds the engine speed until I shift back to 5th. To tell if the converter is locking in 5th, you will see the rpms rise then drop slightly as the converter clutch grabs. You may also hear a change in noise as the engine loads up with this.
@MoabRefugee , I would say the qt low is caused by the fluid entering all the passages in the transmission while warming up. The Torque converters also take some oil as they fill. But as you saw, low fluid/old fluid/too much fluid/wrong fluid can all make this transmission act abnormally. This is especially true for the torque converter.
I checked the fluid cold and hot and it was over an inch past the hot mark. About halfway up the do not overfill writing. Sucks the dealership overfilled it. I hope these have a simple drain plug and I don’t have to drop the pan to drain some out.
To get a good bead on your mpg woes you'll need to check your fuel trims. You may be running rich, in which case you can then start chasing gremlins in the MFI system. Healthy fuel trim numbers should give you 16-19 mpgs.