Automotive Forums

My 1999 GMC 5.7L Z71 has a slightly different variation to all the 4L60-E problems I have been reading online about.  Truck has 121K on it.

I immediately replaced fluid and filter and the pan looked great.  Slightly dusted like a typical used tranny but NO parts or metal chunks in pan.

Here is my scenario...
Truck takes forever to shift 1-2 when babying the throttle, but if you give it moderate throttle it will shift remotely close to normal time span but rather firmly.  If you WOT it the RPMS jump up to 5K and the truck copies a junked out slipping tranny.  WOT does this in all forward gears.  I also caught it not in OD even though OD was selected at the shifter on my way back from OK to IL.  Havent seen it do this since that.  Not 30mins later it had shifted and was in OD.  No codes showed up after many many scans from my autoxray scanner.

Fluid change seemed to improve shifts somewhat, but that is all that changed.  Friend at a tranny shop said that he had seen this before and the fix was to have the ECM main chip(EPROM) erased and reflashed.  Anyone seen or used this fix before?  Id really hate to drop $100 or so for a reflash for nothing!

Or do I have valve body problems like everyone else does?

Dayumned if GM ever gets me to buy a brand new truck from them!