If that is the case, something has broken internally in the transmission and preventing it from turning. It could be the actual parking pawl linkage in the transmission isn't disengaging it.
Since you are removing the transmission, here are the directions. The attached pics correlate with the directions.
2002 GMC Truck Envoy 4WD L6-4.2L VIN S
Vehicle Transmission and Drivetrain Automatic Transmission/Transaxle Service and Repair Removal and Replacement 4L60-E/4L65-E Automatic Transmission Transmission Replacement
- J 21366 Converter Holding Strap
1. Disconnect the battery.
2. Remove the filler tube nut (2) located on the right side of the engine.
3. Raise the vehicle. Refer to Vehicle Lifting.
4. Drain the transmission fluid if necessary.
5. Remove the rear propeller shaft.
6. Support the transmission with a transmission jack.
7. Remove the nuts securing the transmission mount to the transmission support.
8. Remove the Evaporative Emission (EVAP) canister from its mounting bracket on the left inside of the frame to gain access to the transmission support bolts. Do not disconnect the canister lines.
10. Remove the transmission support from the vehicle.
11. Remove the transmission mount bolts (1, 2).
12. Remove the transmission mount from the vehicle.
13. Remove the front exhaust pipe assembly.
14. Lower the transmission to gain access to the top and sides of the transmission.
15. Remove the transfer case, if equipped.
16. Remove the range selector cable end from the transmission range selector lever ball stud (6) and the bracket (1).
18. Disconnect the transmission vent hose, the park/neutral position switch connector, and the main electrical connector from the transmission.
19. Remove the bolt that secures the fuel line bracket to the left side of the transmission.
20. Remove the torque converter access plug.
21. Mark the flywheel and torque converter orientation for reassembly.
22. Remove the flywheel to torque converter bolts. Use care not to drop the bolts into the bell housing.
23. Disconnect the transmission oil cooler lines from the transmission.
24. Plug the transmission oil cooler line connectors in the transmission case.
25. Install a safety chain around the transmission.
26. Remove the bolt that secures the fuel line bracket to the bell housing.
27. Remove the bolts (1, 2) that secure the coolant pipe to the bell housing.
28. Remove the remaining nuts, studs and/or bolts that secure the transmission to the engine.
29. Install the J21366 onto the transmission bell housing to retain the torque converter.
30. Pull the transmission straight back.
31. Remove the transmission from the vehicle.
1. Install the J21366 onto the transmission bell housing to retain the torque converter.
2. Raise the transmission into place and remove the J21366 from the transmission.
3. Slide the transmission straight onto the locating pins while lining up the marks on the flywheel and the torque converter made during removal. The torque converter must be flush onto the flywheel and rotate freely by hand.
Notice: Refer to Fastener Notice in Service Precautions.
4. Install nuts, studs and/or bolts securing the transmission to the engine.
Tighten the studs and/or bolts to 50 Nm (37 ft. Lbs.).
5. Install the flywheel to torque converter bolts. Use care not to drop the bolts into the bell housing.
Tighten the bolts to 60 Nm (44 ft. Lbs.).
6. Install the torque converter access plug.
7. Remove the safety chain from the transmission.
8. Install the transmission vent hose (2), fuel lines, and the wiring harness to the transmission.
9. Install the heat shield to the transmission.
10. Install the bolts securing the heat shield to the transmission.
Tighten the bolts to 17 Nm (13 ft. Lbs.).
11. Install the shift cable end to the transmission shift lever ball stud (6) and bracket (1).
12. Install the transfer case, if equipped.
13. Install the front exhaust pipe assembly.
14. Install the transmission mount to the vehicle.
15. Install the bolts (1, 2) securing the transmission mount to the transmission.
Tighten the bolts to 25 Nm (18 ft. Lbs.).
16. Install the transmission support to the vehicle. Underbody.
17. Install the fuel tank shield.
18. Install the Evaporative Emission (EVAP) canister to the frame bracket.
19. Lower the transmission and remove the transmission jack.
20. Install the nuts securing the transmission mount to the transmission support.
Tighten the nuts to 46 Nm (35 ft. Lbs.).
21. Install the rear propeller shaft.
22. Flush the transmission oil cooler and cooling lines at this time, if necessary.
23. Connect the transmission oil cooler lines (4) to the transmission.
24. Lower the vehicle.
25. Install the filler tube to the stud (1) on the right side of the engine.
26. Install the filler tube nut (2).
Tighten the nut to 10 Nm (7 ft. Lbs.).
27. Connect the battery.
28. Fill the transmission to the proper level with DEXRON III transmission fluid and check for leaks.
29. Road test the vehicle and check for proper operation.
Let me know if this helps.
Images (Click to enlarge)
Sunday, June 21st, 2020 AT 9:05 PM