I am running a 4l80 with a 3400 converter in my truck. The trans has unknown miles but works flawlessly. Lately my converter hasn't been locking up. The converter isn't even a year old with about 5k miles on it. With the converter being so new I'm looking into other possible tcc problems. At light throttle I can hear and feel it try to lockup but more throttle reveals it's not locked. Where should I start for diagnosing this issue?

 

You can pull pan and ohm the tcc solonoid also there is a harness you can purchase for inside of Trans I'd probly ohm them as well. Or just replace the solonoid they aren't terribly expensive.

Solonoid 50-100 olms
Wiring .5 or less

If all that looks good there is a valve in the valve body that could be sticking or has worn the bore out of round causing it to bypass fluid and not lock up. Or simply the clutch in converter is gone.. But before r&r of Trans id try that stuff. Also the o ring seal on solonoid could be gone as well

 

I ran across the sonnax tcc kit in my searching. Looks like I'll be putting a new solenoid, trans harness, and the sonnax kit in. I might as we'll replace it all while I have the pan off. I'm certainly hoping this new converter isn't smoked.