Had transmission replaced recently GMCsierra1998 1500v-6

Circuit/System Verification
Important: If the suspect gage is the speedometer, the drive wheels of the vehicle must be raised and the transmission must be placed in drive or first gear.

1. Ignition ON, with the scan tool, perform the IPC Gage Sweep Test in the IPC Output Controls. Verify that all gage dials move from minimum to the maximum value and back to the gage minimum value.
?‡'
If the gage does not perform the IPC Gage Sweep Test, replace the IPC.

2. Start the engine, with the vehicle drive wheels raised and place the transmission in drive or first gear. Verify that the speedometer value matches the scan tool Vehicle Speed parameter in the ECM/PCM Engine Data List.

?‡'
If the speedometer is incorrect, test or replace the IPC.

use a scanner to reset the CPU as the program is corrupted from the flat battery

You may have a problem with your IPC (Instrument Panel Cluster) which often can be exchanged for a serviced and warrantied replacement unit.

First thing I would try...disconnect the battery for 10 minutes which will allow the on board computers to re-start.

If this doesn't help... I would retrieve any stored codes the on-board computer has logged which may provide a starting point to diagnose your trouble.

You have a serious problem that needs to be check out buy a tranmission shop be for it ouits on you completely.

Definitely not an expert here, but exactly the same symptoms after a clutch replacement. I found one of the wires going to the connector on the harness side of the Vehicle Speed Sensor pulled in two. Can only surmise that during the clutch installation this connector wasn't disconnected and during movement of the transmission to get to the clutch was put under tension causing the failure. I haven't confirmed the solution yet, but pretty sure I'm on the right track.

Your rpm and speedometer cable may broke or come loose from transmission.

I'd wager that the fuse that controls the gauges is shot, or one of the internal connectors got unplugged (Fuse sounds more likely). Radio, Lights, and Turn Lamps are usually on seperate circuits.

Replace the speed sensor located on the top or side of the transmission. Please rate me on this answer.

all chevy made in that year have a speedometer issue i have a 2004 chevy that has the same issue the only way to fix it is to replace the dash insturment panel some of them the speedometer goes and the rest of the gages work fine or try replace the speed sensor located at the front of the transmission on the bottom

I would star by checking the wires and connections for these gages. If they are good then replace the gages.