4l60e won't shift out of 1st.

Trying to help out a friend with a transmission issue. 4l60e won't shift out of 1st until no back of gas, then it shifts fine through all the gears. If you keep on it, it won't shift until around 4 grand, then slams into the next gear. No codes on the scanner, voltage on tips is good, has a new tps converter, neutral safety switch, and it has done this on the old tranny, that we thought was shot, and a brand new rebuilt tranny (2 tranny shops claimed the old one was toast) It will also not manually shift into 2nd. It is for a 98 gmc jimmy, not an lt1, but I was hoping you guys could help. Fluid was flushed and replaced with new trans, including cleaning out of the trans cooler.

any suggestions would be greatly appreciated.

@Cahall

Try putting a scanner on it that can watch data. The scanner will have "1-2 shift" on ot. Watch to see when the computer is commanding the 1-2 shift at varying throttle opening when the problem occurs. If the computer is commanding the shift but it's no happening, you have a transmission problem. If the computer isn't commanding the shift, then you have an external control problem.

Frank

Apparently this was done at 2 different shops, and it had no issue commandingthe shifts.

Also, could the computer be the culprate if we can't manually shift from 1st to second?

What year is the vehicle? Did the shop rebuild the original transmission?

Frank

His vehicle is a 98. The new transmission is a rebuild from a 2000 s10 I believe.

If the computer is commanding the correct shift timing, but it's not shifting, it's most likely a transmission issue.

Frank

Yup, was rebuilt and put in the 2000 s10 4x4 and ran fine. Its still under warrenty. For 90 days from the shop that rebuilt it.