I rebuilt my 4L60E trans (First 4L60 I've done) and have very soft/slipping 1st and 2nd gear.

Symptoms are
1) Very soft slipping 1st and 2nd (Didn't take the truch over 20MPH)
2) Putting in first can cause a chatter like the park pawl trying to engage.
3) Reverse is solid.
4) Putting in 2nd causes the trans to try to lock.

sounds like when someone rebuilt that transmission, they didnt do a very good job on ur 1-2 clutchpack, could be they put to many clutch disks in there, didnt line them all up, left a snap ring out, put the piston or piston seals in there wrong, if it dont fix itself, then ur will ahve to have it tore back apart

sounds like when someone rebuilt that transmission, they didnt do a very good job on ur 1-2 clutchpack, could be they put to many clutch disks in there, didnt line them all up, left a snap ring out, put the piston or piston seals in there wrong, if it dont fix itself, then ur will ahve to have it tore back apart

Actually the connection to the computer was not fully seated.

The 1-2 shift solonoid was damaged (partially shorted) during assembley.
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The trans has over 1000 miles now without complaint, including some heavy hauling and hill climbing.http://www.automotiveforums.com/vbulletin/#