4L60E tranny problems

1993 Z71 with a 4L60E trans. lost all but 1st and 2nd gear little over a year ago while pulling a 15' boston whaler. Replaced with a new heavy duty 4L60E transmission and put @10,000 miles on it and it has done the same thing while pulling a gooseneck trailer. attempts to shift to 3rd but "slips" and the engine just revs up. Any suggestions would be appreciated.

With only 10,000 miles since installed it may still be covered under warranty?

im having the same problem, mine went when i was hauling a 63 chevy. From what i've read in a bunch of posts its probably something electrical. it could be solenoids, but on mine (and a another guys post i saw) the speedo needle goes crazy and then stops working, and the brake light comes on. Im still a little confused as to what exactly he did to fix it (and it did fix it) but it had something the do with the acc power wire for the speedometer. I guess the electronics for the tans use information from the speedometer to control shifting. I just saw this post today, and i'm checking it out first thing when i get home, i'll keep you posted on my "findings"

OK so i was reading up on other forums and found this. dear God i can't wait till i get home and check this out!
 





I have a 1994 Firebird that has the 4L60-E Automatic Transmission.

On the same day my transmission quit shifting, (all gears) my speedometer also quit working. All the transmission people tell me I need to re-build my transmission.

I am not buying that the ELECTRONIC transmission that relies on the car speed to shift and the speedometer both going out at the same time being independent problems.

I suspect it is the PCM or the speed sending unit. I do not know exactly how the PCM gets speed information used to shift. Does this input come from the transmission or how can I determine if the PCM is getting the car speed?

Would this information be in the diagnostic codes? (With the car not moving while testing for ?can you read car speed? would this be a test?)

It is my understanding that the speedometer itself is just a analog meter displaying what the PCM tells it to, (not the sending unit to the PCM) the PCM must get an input from somewhere, (thinking straight from the transmission) and that is the part I need help with.

I need to determine if the PCM is getting the speed input it needs on the current car speed but do not know how to determine that, not knowing exactly where that input comes from.

Anyone have a speed sensing problem cause 4L60-E problems?

Any Help would be GREAT!

Thanks!