In my 95 GMC Sierra 1500 4x4 just had the transmission rebuilt 3 weeks ago I was driving down the road and it shifted 1st to 2nd fine but from 2nd to 3rd it reved up all the way to 4500 rpms before shifting to 3rd and won't shift 4th gear wat could that be?

Sounds like it needs to go back to the shop that rebuilt the transmission.

I suggest taking it back to the shop that rebuilt it.

Solenoids inside the transmission or the control module.

1 Ck A/T fluid level & quality
2 Scan/ck for code(s)
3 With scan tool connected,road test vehicle/Ck parameters....
....time for a pro !!

If you need further help, reach me via phone at https://www.6ya.com/expert/ralph_2f0886b7d6af32ce

could be the switch on the trans or the pump may have went out, or something is wrong with the valve body inside the trans

rec check fluid first. If trans fluid hasn't been changed in last 30,000 miles change fluid, filter and pan gasket. At that time inspect for foreign materials in bottom of pan or on magnet if you have one. If truck has over 100K and fluid was never changed you may have more problems if changing the fluid.

-----check possible tps [throttle position sensor ]circuit for damage or faulty sensor----if good check the fuses and trans harness for shorts damage or disconnection,check o2 sensors wiring possible ground to exhaust ,or internal leak 2nd gear apply circuit[servo assembly or 1-2 accumulator] or poor pump pressure

3RD & 4th shift solenoid is bad inside the transmission

no power stuck in 3rd gear electric shop unless youve burnt it up good luck...www.TransmissionGarage.com

SHift solenoid pressure switch