my 2000 gmc sierra 1500 2wd 5.3 engine wont shift into 3rd or 4th or overdrive wont down shift when you stop the light for gear selector flicker gas gauge doesnt work right any help

Do the brake lights work? If not replace the brake light switch. It controls the Lock up/ overdrive. Have you had the tranny fluid changed? Could also be the 3-4 shift solenoid

yes the brake lights work but my transmission went out and i replaced it with a rebuilt transmission and it was still doing the same thing so i took it to where i bought the tranny so they could check it out for me they said they replaced a solinoid and the internal wiring harness put it back together and as soon as it shifted into second gear check engine light came on and transmission freeze up in second they told me i had a electrical problem they said it keeps blowing that same soilinoid

yes the brake lights work but my transmission went out and i replaced it with a rebuilt transmission and it was still doing the same thing so i took it to where i bought the tranny so they could check it out for me they said they replaced a solinoid and the internal wiring harness put it back together and as soon as it shifted into second gear check engine light came on and transmission freeze up in second they told me i had a electrical problem they said it keeps blowing that same soilinoid