2000 Oldsmobile Bravada Speedometer

First thing you need to do is have the codes read, Post the results with the code number(s). Even if the service engine light is not on, there should be freeze frame data stored.
If it won't make it, buy a cheap scanner, they can be had for 30-40 dollars, a good investment, since they cover all cars sold in the USA from 96 on.
If the light is blinking, it means possible damage to the converter. Service it right away!

This is all I found on what seems to come close to your problem, did the autozone scan tool power up? Or no readings?
Malfunction Indicator Lamp (MIL) On, Transmission Stuck in Second or Third Gear, Instrument Cluster Inoperative (Verify and Repair Source of Voltage Loss In Transmission Solenoid Power Supply Circuit) TECHNICAL SERVICE BULLETIN Reference Number(s): 01-07-30-002E, Â Date of Issue: Â September 23, 2005 Related Ref Number(s): 01-07-30-002A, 01-07-30-002B, 01-07-30-002C, 01-07-30-002D, 01-07-30- 002E ARTICLE BEGINNING CONDITION Some customers may comment on one or more of the following conditions: Ã Â Â The Malfunction Indicator Lamp (MIL) is ON. Ã Â Â The transmission is defaulted to second gear (4L80/85-E). Ã Â Â The transmission is defaulted to third gear (4L60/65-E). Ã Â Â The instrument cluster is inoperative. Upon investigation, one or all of the diagnostic trouble codes (DTCs) P0740, 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 solenoid power supply circuit. This condition may also be the result of an incorrect installation of an aftermarket electronic device such as a remote starter or alarm system. CORRECTION Affected Model(s): 2006 and Prior GM Passenger Cars and Light Duty Trucks; 2005-2006 HUMMER H2; 2006 HUMMER H3; 2005-2006 Saab 9-7X; with 4L60-E, 4L65-E, 4L80-E or 4L85-E Automatic Transmission (RPOs M30, M32, M33, MT1, MN8) Supercedes: This bulletin is being revised to update model years, add additional models and add additional diagnostic information. Please discard Corporate Bulletin Number 01-07- 30-002D (Section 07 -- Transmission/Transaxle). IMPORTANT: If the vehicle is equipped with an aftermarket electronic device and the DTCs are being set when the device is being used, verify that the appropriate fuse is being supplied battery voltage during operation. If voltage is not present at this fuse, these DTCs 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 the system for corrections. ANY1. With the ignition switch in the RUN position, test for battery voltage at the circuit fuse in the transmission solenoid power supply circuit. Refer to the appropriate SI Document for the transmission solenoid power supply circuit information. 2. If battery voltage is present at the fuse, inspect the ignition voltage circuit between the fuse and the transmission for possible opens. 3. If battery voltage is not present at the fuse, test for continuity between the fuse and the ignition switch. If NO continuity is between the fuse and the ignition switch, repair the open in that circuit. 4. If you have continuity between the fuse and the ignition switch, the most likely cause is the ignition switch. Replace the ignition switch using the appropriate Ignition Switch Replacement procedure in SI. Refer to group number 2.188 of the parts catalog for part description and usage of the ignition switch. REPAIRS DUE TO AFTERMARKET INSTALLATION OF ACCESSORIES IS A NON-WARRANTABLE ITEM.