I have a 2003 gmc sierra 4wd, my tranny is not getting 3 or 4 gear, replaced it with a used one,and you its,doing the exact same thing I can drive great in 1&2 but in 3 it slips and won't go into 4th.
Should take to someone with a code analyzer than can read trany codes, that should tell you what is going on...
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