My '03 chevy 1500HD(6.0) doesn't shift from 3-4 if you stay on the accelerator. If you back off the gas and "help", it shifts ok. Would changing the fluid & filter help? What about additive for "sticky" valve? Thanks

My '03 chevy 1500HD(6.0) doesn't shift from 3-4 if you stay on the accelerator. If you back off the gas and "help", it shifts ok. Would changing the fluid & filter help? What about additive for "sticky" valve? Thanks

I just checked into this problem of no 4th gear 4l60-e...this can be many things in and out of transmission...

check the connector on the side of the transmission for damage and corrosion...

yes valve deposits and debis interfering with the operation as well as wiring and switches and sensors and etc....it goes on and on...diagnostic is best with the correct scanner..

Thanks J Cat --- would a scan tell me anything if the "check engine" light is not on?

Thanks J Cat --- would a scan tell me anything if the "check engine" light is not on?

the dtc scanning of the drive train is needed..this would be manufacturer specific...so not all scanners are capable of this...transmission shop should be able to correctly get this dtc..with the correct equiptment..

the check engine LT is just that ,,,engine..as service 4wd lt is to the transfercase etc...