What's wrong with my gmc envoy

Driving 65 mph let off gas to go around turn when I gave it gas again nothing
just revved motor no sounds no engine light no codes at all had it towed  they
told me needed a new tranny they wanted 3500.00 said no towed home they
had dropped my tranny pan drained fluid took out filter and have way put it
back on DID NOT tell us. We bought a rebuilt tranny a new convertor put in
and still will not move goes in gear but just revves up. Have been told maybe
a sensor or it needs to be flashed by dealer. Please help 1600.00 in it so far