1998 GMC Sierra...still won't shift right..

[Greywolf0723]

1998 GMC Sierra 4x4 4L60E transmission

I replaced the transmission. Before and after I replaced it I am having the same problem. When I start the truck, everything is fine. I drive, and when it is time forthe truck to shift into 3rd gear the check engine light comes on, and the transmission goes into a "safe mode" and remains in 3rd gear unless I manually downshift. It will not go into overdrive. After checking everything that the TSB told me (it is in the chevy forum here), and I took it to someone to help troubleshoot, I am still puzzled. The TSB said to check voltage at the #20 fuse, which is to the transmission. I did that, and then I even checked at the plug going to the trans. Both have 12v like they are supposed to. I also replaced the module that sits on the driver's side of the tranny. I purchaced the kit where it comes with new plugs which I soldered in place. (There was a problem with the plugs melting in place and causing a bad connection) All connections have been tested good on the plugs. Could this be the PCM? Could it be that black box on the driver's side is not adjusted right? I am going to replace the ignition next; however, I am not confident that it is the problem. After that I will go to the junk yard and get a PCM and try that. I do not know what else to do. If you have a better way to go, please let me know. Thanks

[mphmilkman]

a few things you should know. The black box on the linkage should be your neutral safety sw and reverse lights. The problem should not be related to this. If you get a pcm from salvage you may regret it. It would have to come from the exact same truck with the same options and year. You can get a reman and have the program installed for your vin and that would be better. The pcm is less that 200 and the programming should be around 100. Go to advanced auto and get the DTC for the transmission that is lighting the service engine soon light.

[horse482]

TSB# 01-07-30-002D

Malfunction Indicator Lamp On, Transmission Stuck in Second or Third Gear, Instrument Cluster Inoperative.

04-05 Rainier
99-00 Escalade
02-05 Escalade and EXT
03-05 ESV
97-99 Chevy/GMC Full Size; Pickup, Suburban, Tahoe (Yukon) (Old Style)
97-05 Blazer (Jimmy), (Bravada), Corvette, Express (Savana), S10 (Sanoma)
99-05 Silverado (Serria) (New Style)
00-05 Suburban, Tahoe, Yukon, Yukon XL
02-05 Avalanche, Trailblazer, EXT, Envoy, XL, XUV
04-05 Colorado/ Canyon
03-05 H2
04-05 GTO
With 4L60-E, 4L65-E, 4L80-E or 4L85-E

Condition: One or more of the following problems:
- The Malfunction Indicator Lamp is on.
- The transmission is defaulted to second gear (4L80/85-E).
- The transmission is defaulted to third gear (4L60/65-E).
- The instrument cluster is inoperative.

Possible DTC’s: P0720, P0753, P0758, P0785, P0787, P0973, P0976, P1860, P2761, P2764, and P2769 may be set depending on the vehicle.

Cause: The most likely cause of this condition may be a loss of voltage to the transmission on circuit 1020. This loss of power may be caused by an open in the ignition switch. This condition my also be the result of an incorrect installation of an aftermarket electronic device such as a remote starter or alarm system.

Correction: With the ignition switch in the RUN position, test for battery voltage at the appropriate fuse listed below.
97 S/T Trans 24
98-05 S/T Cluster 11
02-05 S/T Ignition 0
97-00 C/K(Old) Trans 20
99-05 C/K(New) Ignition 0
97-02 G-Van Trans 20
03-05 G, H-Van Ignition 0
03-05 H2 Ignition 0
04-05 GTO Auto Trans
97-04 Corvette Enging 1
05 Corvette ACC/TCM
04-05 Colorado/Canyon Trans

If the battery voltage is present at the fuse, inspect the ignition voltage circuit between the fuse and the transmission for possible opens. If the battery voltage is not present at the fuse, replace the ignition switch.

If the vehicle is equipped with an aftermarket electronic device and the DTC’s are being set when the device is being used, verify that the appropriate fuse listed above is being supplied battery voltage during operation. If voltage is not present at this fuse, these DTC’s will be set due to lack of voltage at the solenoids. This condition is most likely to occur with an incorrectly installed remote starting system. If this is the case, refer the customer to the installer of they system for corrections.