Nissan Repair: Automatic Transmission, r b reed, cottman transmissions

Question
I have a 2000 Nissan Maxima GLE that I bought new. While driving I-80 across the Sierra's at speeds between 65 and 80 (traffic speeds) A/C on, 90 degree outside air temp. On an upgrade 5% or so, the car downshifted the engine revs went to 5200 and car gained no speed, when grade flattened out, car downshifted into 4th, but no 4th. revs went to 500 and car continued to coast at 70 or so. When accelerator advanced the engine speed came up to 4000 or so and engaged 3rd gear. I tried 3 times to engage 4th gear but could not. the problem began at about elevation 2000 ft and at 6000 ft I pushed the O/D out button and continued on at a slower speed to the next town. After stopping in Truckee to look for a Dealer, I restarted the car after 15 minutes or so, problem went away. Repair people said they can't fix it unless it occurs again. Now concerned that it may return at an inoppurtune moment. Could there have been some overheating of the transmission fluid causing this symptom? This has been a good car and this is only the 2nd problem I've had with it. The other was unrelated. Please give me your thoughts. Thanks for your time. R.B.Reed

Answer
Hi Richard,

My first thoughts are that the transmission is headed for an overhaul. If there is a check engine light on, then we might be able to repair this with a sensor, solenoid or other electronic device. Turning the key off resets soft codes in the computer and things will run fine until it sees a problem again. If the CEL was on then there will be a stored code in the computers memory that we need to retrieve. I suggest taking your car to a shop that can scan the computer in your car and let me know what, if any, codes they come up with. By number, please. Cottman Transmissions will do this for free.