98 1ton tcc unlock issue

[hcaliber]

Hey guys I have a 98 1ton gm truck with the 5.7l and I assume it's the 4l80...around 300,000kms on it. I bought it used with this issue. 

Problem is I can drive all day under 60mph and everything is fine...if I do 60 or over for more then a minute or so the tcc unlocks slightly... A few hundred rpm...and will not lock again until I restart truck. If I plug in scanner while driving and clear codes tcc locks in seconds. Only codes that are there are a few o2 sensor and a steering assist...this is using an updated efi live scanner...now I have checked speed sensors... One in tcase had some metal fillings on it I cleaned off but no help. Wires and harnesses look good... 

Fresh oil in transmission as well 

Any suggestions to besides take it to the dealer? 

Thanks, Lyle.