1998 Silverado Transmission???

[firebird0095]

I have a 98 Z71 with the 5.7L. When it is in overdrive and you are going about 40-47/48 - if you push on the gas it rattles and then downshifts and it is fine. If it is in overdrive and you are going faster than 50 or so there is no noise at all. Other than that there are no problems with the transmission or the 4X4. I am not familiar with automatics at all, as I have always had manual sports cars. It kinda sounds like synchronizers rattling(does it even have them). Not knowing how my transmission works it is hard for me to hear what is happening. I have been told that you can reprogram it and it will stop that. Is that BS, and if it is true then how much will something like that cost. When I got the truck used, the dealer had replaced the engine/transmission cooling line because the Check engine light was on. Now the light is on again, and the same noise. I am guessing they are related. Any help would be great. Also, I am in central Indiana - so where are there good and affordable shops?

Thanks
Mark

[Jeremy-WI]

Go to Auto Zone or anyplace that will read codes for free and post the code. There could be a reflash for your PCM that would change your shifting, might even be able to do it yourself with a hypertech

[firebird0095]

I went to the dealer and they read the codes for me for free. It turns out that the light is on bacause of a plugged cat, and not because of the tranny. If anyone has any ideas on this let me know. Also, I have been playing with the noise a little. When it makes the noise, if i keep my foot on the gas and tap the brake with my other foot it unlocks the converter and downshifts right away. Also, I get it to make the noise and then pop it into third and the noise stops right away. From what I understand, the only difference between third and fourth is the band and a clutch. I am trying to figure out what could make a rattling noise like that. Someone suggested a broken planet, but I think it would be more of a grinding noise, and a lot louder if it were that. Anyway - any ideas - let me know.

[tommie99]

sound to me you have a broking sun shell that is a hard part inside you trans............tommie99