Transmission Problem

Have a 2003 Envoy xl SLT 4x4, was driving yesterday and heard a loud clunck when taking off from stoplight and accelerating. Envoy RPMs would rev to between 3-4,000 before shifting at around 30 mph. Higher speeds it drives fine. Took to CarX they said trans issue and refered to Transmission shop. They said gears 1 and 2 gone, and will need a rebuilt trans at cost of $1800-2100. Does this sound right?

Yes.