Make sure the gear selector cable is on tight and all brackets are in place. Inspect motor mounts for excessive play.
Hopefully it is a simple thing like a loose selector cable connection to trans.
You do not want the trans to continue slipping, this will ruin it.
I would take it back to whomever installed it and get it diagnosed/repaired.
If it was a rebuilt trans, it should have a warranty, if used the warranty generally only includes a replacement trans (not labor).
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Sunday, November 9th, 2008 AT 9:30 AM