94 chevy 1500 5.7 was not shifting from 2nd to 3rd rpms would just rev high. I bought a GM OEM 4L60E and it worked fine for one week and then started same problem, no 3rd or 4th. Could it be something besides a bad luck. Can anything else outside of tranny cause this issue? Help....

 

Was it modified at all? Sounds like something may have caused low line pressure and you smoked the 3rd and 4th clutch pack.

 

The driver

You said the first one did not shift from 2-3 and the second lost 3-4.

If that's the case, most likely bad luck.

Here are some things to consider. When a trans fails you need to flush or replace the cooler. Same with the Stall converter. Other wise the contamination especially metal can cause the next unit to fail.

If the second unit was a new/re manufactured GM 4L60E, GM will not honor the warranty if you can not prove those items were replaced when replacing the original failed unit with a new unit. At the dealer they use a trans flush machine to clean and check the flow of the cooler. If it does not meet spec the cooler must be replaced. In some cases the lines have to get replaced as well.

Since most trans coolers are usually in the radiator with there occasionally being and external cooler like with a towing option, This would mean the radiator has to be replaced as those coolers are not serviceable.