1993 Chevy Suburban shifts incorrect

Hello .. thanks for the donation .. much appreciated

If the CEL is not on, Does not mean there are no transmission codes stored .. not all fault's will light the CEL .. please check for codes and repost with your finding's/codes for more assistance !

RETRIEVING CODES (WITHOUT SCAN TESTER)
Turn ignition on. DO NOT start engine. TRANS or SERVICE ENGINE SOON light should glow. Locate Assembly Line Data Link (ALDL) connector under dash, on driver's side of vehicle. Turn ignition on with engine not running.
Connect jumper wire from terminal "B" (diagnostic terminal) to terminal "A" (ground terminal) of ALDL connector. See Fig. 8. Some models do not have a wire connected to "B" terminal. These models must use a Scan tester to access trouble codes.
NOTE:Connecting terminals "A" and "B" of ALDL connector with engine running will cause fuel injected vehicles to enter field service mode. The TRANS or SERVICE ENGINE SOON light will not flash codes if this is done.
Fig. 8: Identifying ALDL Connector Terminals

TRANS or SERVICE ENGINE SOON light should begin flashing codes. Each code will be repeated 3 times. Code 21 is identified by 2 flashes, a short pause followed by one flash; Code 53 is identified by 5 flashes, a short pause followed by 3 flashes. Trouble codes are separated by slightly longer pauses.
Trouble codes are displayed in numerical order. Each code is displayed 3 times. Codes will continue to repeat as long as ALDL test terminal is grounded.
If codes are not flashed, or TRANS or SERVICE ENGINE SOON light does not glow, self-diagnostics will not work. See CHART A-1 under DIAGNOSTIC CHARTS. If TRANS or SERVICE LIGHT SOON light glows steadily, see CHART A-2 under DIAGNOSTIC CHARTS. To exit diagnostic mode, turn ignition off, and remove jumper wire from ALDL connector.
NOTE:Trouble codes will be recorded at various operating times. Some codes require operation of sensor or switch for 5 seconds; others may require operation for 5 minutes or longer at normal operating temperature, road speed and load. Therefore, some codes may not set in a service bay operational mode, but may require road testing vehicle in order to duplicate condition under which code will set.

RETRIEVING CODES (WITH SCAN TESTER)
NOTE:To read trouble codes and check system voltages on serial data line, plug scan tester into ALDL.

The scan tester is a specialized tester which, when plugged into ALDL, can be used to diagnose on-board computer control systems by providing instant access to circuit voltage information without need to crawl under dash or hood to backprobe sensors and connectors.
Scan testers may also furnish information on status of output devices (solenoids and relays). However, status parameters are only an indication that output signals have been sent to devices by the control module. It does not indicate if devices have responded properly to that signal. This will need to be checked at output device using a voltmeter or test light.
NOTE:Code 12 should always exist when ALDL is grounded with key on and engine off, but may not be indicated by all makes of Scan testers.

If trouble code is not present, this is not an indication there is no problem. Driveability-related problems with codes displayed occur about 20 percent of the time, while driveability problems without codes occur about 80 percent of the time.
Out-of-specification sensors WILL NOT set trouble code, but WILL cause driveability problems. Using scan tester is the easiest method of checking sensor specifications and other data parameters. Intermittent wiring problems may be identified by wiggling wiring harnesses and connections (key on, engine off) while observing scan tester.

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