Rough downshifting from 2nd to 1 st gear uphill

Hello, first, the transmission fluid should be at least drained and refilled approximately every 30,000 miles. If it has never been serviced at 206,000 miles, it's a double edged sword. You may induce issues by introducing fresh fluid to your well worn transmission. This is quite different than a "transmission (getting) used to the fluid in it" -- it's not used to it, it's just that there is likely particulate debris within your transmission that could get stirred up when diluted with fresh fluid. Do not "flush" or "exchange" all your transmission fluid at this point, regardless. Your transmission fluid has necessary agents and friction modifiers in it that help with proper clutch operation. Over time and mileage, these agents deteriorate. As a result, your transmission typically will not operate properly in the long run. All that said, your concern doesn't sound like something that can be rectified by changing transmission fluid or servicing at this point. Ensure your fluid is full when properly checking at operating temperature. It can also be that your internal components have wear -- backing up a grade from a stop can be taxing on transmission reverse clutches if the transmission has some time and miles on it as it is. Being that your vehicle is 15 years old with 206,000 miles, and you are having the symptoms you describe, it's reasonable to deduct that there are probably larger repairs in your fairly near future. I do not, by the way, think you have any electronic transmission issues. The only other thing to consider is that the load the engine processor is seeing on the transmission at that moderate to steep grade at slow speeds warrants a downshift, and that possibly low fluid level and/or poor fluid condition could be affecting smooth operation.

Quiz the dealer service manager or even a local transmission specialist about a service bulletin on a leaking supply tube inside the transmission that may cause these symptoms - this can be intermittent and IS more pronounced when transmission is hot and vehicle is being reversed up grade.. Produces more of a jerking sensation that is felt throughout the vehicle.. This however does not normally affect transmission downshift .. I owned 2002 that had this problem is the only reason I chimed in here. BTW - it reads on a label wrapped around the top of dipstick - under normal conditions transmission fluid doesn’t need to be serviced - that’s not a recommendation on my part - just what Toyota states The fluid level certainly need to be correct! Good luck!