GMC Trailblazer transmission wont shift from 2nd to 3rd. Ran low on fluid!?

Have a 2003 Trailblazer. Had a tranny leak I didn't know about. Fixed the leak, filled it up with tranny fluid. Will shift from 1st to 2nd. I can get it into 3rd if I push the accelerator very hard, never 4th. Had the codes ran at a local shop and they found no errors. Any ideas of what the problem is? Thank... show more Have a 2003 Trailblazer. Had a tranny leak I didn't know about. Fixed the leak, filled it up with tranny fluid. Will shift from 1st to 2nd. I can get it into 3rd if I push the accelerator very hard, never 4th. Had the codes ran at a local shop and they found no errors. Any ideas of what the problem is? Thank you so much!
Update: Ran 5 quarts low.
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