1997 k1500 gmc erratic speedometer/tranny shifts

[zerowheelspin]

1997 gmc 1500 z71 4l60e 5.7L 125000miles on the clock
this thing is messing with me. back in '07 i had a fresh gm 4L60E put in my truck. well just a few weeks ago i noticed it kicks out of over drive and will not re-engage finnal lock untill its shut off and let cool. i used my snap-on brick scan tool to check it and found no codes. i did notce that while in overdrive lock it see about 80-190rpm slip. i was told that it should be 0 to maybe 5rpm slip at the tops. the trans is still under warranty but i see another problem.
as of late my speeometer is acting up. when shifting from rev. to drive it will jump to 35-60mph but the truck has not even moved yet! i got into the ABS side and checked the rear vrs the front 2 sensors, and they read the same while moving. when i stop the front read 0 and the rear slows down to zero, but then jumps up to 50mph or so if i let off the brakes even to inch forward. this then makes the trans shift from first gear to second or even third while still stopped. when i do let off the brakes to go on my way it snaps back to first and then acts normal. ??????????

[transman618]

Whats the VSS reading on your scanner say? You might need to change the VSS on the tail housing of the transmission.


transman

[zerowheelspin]

did that, made it a little worse. it seems to keep going after you stop. i really don't know how.

[zerowheelspin]

i got it! so i could not just let it go so i started to check all the connetions from the rear speed sensor forward. i found a set plugs thats not on all-data diagram. i followed these wires back to the cab through the fire wall to a "jet scu 2000" speed control unit. so back when i paid a shop to recalibate the speedo they just put this thing in and stuffed it way up in the dash. this unit is whats causing all the problems.
any one ever used one of these jets units? ever had or are now having the same problem as i was?

[transman618]

Originally Posted by zerowheelspin

i got it! so i could not just let it go so i started to check all the connetions from the rear speed sensor forward. i found a set plugs thats not on all-data diagram. i followed these wires back to the cab through the fire wall to a "jet scu 2000" speed control unit. so back when i paid a shop to recalibate the speedo they just put this thing in and stuffed it way up in the dash. this unit is whats causing all the problems.
any one ever used one of these jets units? ever had or are now having the same problem as i was?

Thats interesting. Glad you found that.


transman