1999 Tahoe,possible trans or switch problem! need help

I have a 99 tahoe that I took to the shop to have the transmission rebuild less than a year ago. Yesterday, as I was driving I stepped on the gas pedal, but the truck would not accelerate. The rpm would go up, but no response. I checked the 4x4 switch to make sure it was on 2hi, however the light next to it was not on.I took the part off and tested it on another tahoe, the part does not work. DO you think that this happened because of the faulty switch? or is it the transmission again? Is there any way that if the switch does not work, something like this could happen? I hope its the switch and not the transmission. Thanks in advance

I would check the fuses...with a meter..

if the transmission slips in gear the fluid will look dark and have a bun't smell..If so the transmission is bad , again...

when this was repaired the last time did they replace the torque converter ? clean out the tranny coolant/radiator lines...if not this is a reason why your at it again..