Really weird shifts/non-shifts HELP!
96 Bonneville SSEi, 212,000 miles. Factory stock, did a heater core install and soon after noticed intermittent electrical issues with the radio display (display shuts off, radio shorts out then restarts, automatic climate control indicates it'* working but nothing from the blower motor) but the car otherwise ran fine. Then it lost an alternator, replaced that with no issue. Soon after that, the transmission began to slip in the lower gears. Not all the time, but it was more noticeable when taking off on hills. Fuel consumption went through the roof (average 11.5 mpg). Thought I might have a bad O2 sensor and maybe a clogged transmission filter. Changed out O2 and dropped the pan to replace transmission filter and fluid (first mistake). So far, only codes were a P0301 and a P0171. Swapped out bad coil and cleaned throttle body. Removed throttle body screen in front of the MAF (old trick from my Firebird days). No more codes, or so I thought, intermittent P0171. Anyway the transmission slipping gets worse, now it will not move unitll you rev it over 1500-2000 rpm, and it will hold first and second gears until well past 4000 or u force a shift by lifting the throttle. Does not matter if I force a manual 1st or 2nd gear start or leave the gear selector in OD. Checked for codes with my Actron code reader, no codes other than the intermittent P0171. I'm pretty much resigned to replacing the tranny, but.. Every now and then, the clouds part and the dang thing drives like nothings wrong. I disconnected the battery and the ECM/BCM connectors so the computer would defaut to factory and hopefully "unlearn" whatever is causing the transmission to bind up. No luck, and no new codes either. Anybody have any idea what may be causing this?