After searching through about 8 pages of post I didn't see any post on similar issues. So here'goes.

1999 Silverado 5.3 Z71 auto track/ 4L60e 153K miles

In the mornings, on my drive to work the converter locks up fine at around 65mph (or whatever hwy speed). After warming up, the converter will unlock and the RPM's will raise 200rpm or so.

If I accelerate or start climbing a hill the converter will lock up, but unlock whenever the load is relinquished.

I did just buy this truck, and it has started to run rough in the mornings or on cold start ups. No ses light yet, but there is def a misfire with a cold start.

Sound like the misfire could cause the converter to not lock up? What has me confused is that it does lock up in the morning when the trans is cold and the fluid is possibly thicker? So maybe it could be a pressure problem?

Any help or direction would be appreciated. I'm working on finding someone with a moddis or tech2 that can tell me if the TCC is being commanded off or...?

 

missfire will cause the TCC to unlock
p0300

 

check and see what codes are thrown in the PCM

 

would a basic scan tool be able to read stored codes?

 

Ive had a similar problem for a while. Never throws codes.

 

Valvebodys wore out we had a ton of problems with 96-99 valvebodys doing this exact same complaint. You may or may not get a p1870 trans slip code as well sometimes.

I'm not saying this is your problem but it is exact to problems we learned the fix for the hardway back when.

 

Trans temp?

 

Yea I used to have the same problem. Turned out that my factory cooler was busted and was causing the trans to overheat which caused the unlocking issue and was getting a slippage code. I bypassed my fractory cooler and put on an external cooler. Never had a problem after that.