My steep driveway is about 15 degrees and 70 ft long. My 223k mile 2005 MDX (usually in D5) would decelerate to a stop somewhere on the hill. Even if I floor the gas, engine speed doesn't go beyond 2000 rpm. After I rev the engine for some time (less than a minute), A/T TEMP light comes on. The car would still climb after I shift to 1. I think the transmission fails to down shift when climbing a hill, stuck at certain high gear, clutch slips, and ATF temperature goes way up. Other than this, driving on local streets and highways is still normal.

I looked up the Automatic Transmission Symptom Troubleshooting Index in the service manual but couldn't match my problem with a listed symptom. I plan to pull DTCs at O’Reilly tomorrow but doubt I'd get any as D5 didn't blink; MIL (Check Engine) didn't come on.

Any help in diagnosing the problem is appreciated! If a diagnostic tool may help, would you please recommend it?