No Second Gear and No Speedometer

Josh16 · June 2, 2021

I have a 2004 Chevrolet Silverado 1500 4wd with the 4L60-e 4 speed transmission. Currently I have no speedometer and despite the transmission shifting very well, it skips second gear consistently (no intermittent functioning). This is the ONLY gear that it has issues with (reverse and the rest of the gears are good). Here is the story... I bought this truck being told the transmission was shot. Initially it would not shift past 1st and also had a functioning reverse. I had the tranny swapped with an equivalent from a suburban. It improved slightly but still there is no speedometer or second gear. NO ENGINE CODES have come up throughout this entire time including prior to tranny being swapped (this includes no ABS lights).

Here are the different problems I have found on the internet that I have tried to rule out:

VSS- A mechanic with a good computer states that all 3 Vehicle Speed Sensors read correct speeds in real time on the road
Ignition switch- Already changed
Fuses/relays- All appear to be intact and functioning
Dash cluster- broken connections fixed restoring all function besides speedometer
Transmission treatment- Lucas treatment put in in case this could be a sticky solenoid to no avail
Grounds- All appear to be in excellent condition and no frayed wires visible
Low Voltage- New battery in place

Help me out! What I can see as being my next options are either changing out the ECU or the wiring harness, neither of which I am desiring to do. Any recommendations from your experience that I may have missed in my internet reading?