Since it sounds like you let the tranny downshift on its own, it may have gotten hot. Do you have a tranny fluid cooler installed? If not, get one installed with a fan to pull air through it and you will probably want to install an engine oil cooler, also with a fan, while you are at it. I never let our MH get too low on RPMs before I manually downshift the tranny. One looses too much momentum waiting for the tranny to shift on its own, which is hard on the tranny, so it gets hot. We run at 3000 RPMs on the freeway (62 MPH according to the GPS) and when we have to start pulling passes I downshift at 2000 RPMs, which moves us back up to close to 3000 RPMs. We have not yet had to go to first gear, 2nd seems to have all the power we need with our 454 for all the passes we pull while going to Montana.
No I think Lakota has made a good point in the fact that the 727s will hunt gears. Manually shifting the tranny should help that hunting problem.
Using the lower part of the radiator is not the same as an auxiliary tranny cooler. All it is doing is sending hot fluid into a radiator that is running at 195 degrees or hotter, not very effective at cooling the tranny fluid. I by passed the radiator when I installed our tranny cooler just to keep the radiator heat from effecting the tranny fluid.
David, we have lived in MT and the Dakotas where the temps would get to 40 and 50 degrees below zero, and the automatic transmissions would shift just fine, it was the manual ones that would be a problem getting to shift as that 90 weight gear oil was like grease till the tranny operated for a few blocks to get the gear oil loose enough to shift gears. That is one of the reasons I always parked the trucks backwards so I could leave it in a forward gear to get moving in the mornings.
I understand you were in the cold and still driving fine. thats why I was puzzled by what I had read years ago about the tranny not shifting if you remove the radiator hookup. I just posted because that was the teaching I had recieved back in the day. I was just thinking about band or clutch pack pressure if the viscosity had thickened from the cold and maybe they would not apply with as much force as required and maybe cause premature wear. But, Im always accused about thinking things to death. Might be worth a second opinion from an expert...
One thing that probably helped is that all our vehicles had carbs and we had to wait for the engine to warm up some and that was enough to get the tranny loosened up so there was no hesitation starting out or problems shifting. We were in warmer climates by the time we got our first fuel injected auto so we do not have any experience with FIs in 40 and 50 below weather. Which I am not sorry about. LOL
I just had a thought. the publications I was reading back then were car performance mags. quite possibly the weight of a motorhome and the extra heat generated by the tranny torque converter with those loads is enough to deal with the cold.
Now that would explain the difference, performance trannys are built differently than stock ones because they are built to handle the high power output of performance engines, not the everyday driving standard auto are subjected to.
I would still chat with a local old weather tranny guy...what could it hurt?