I have raised the lockup point to 255mph for TCC in 3rd, thus allowing Torque converter to continue functioning in direct gear.
Any downside ?
Will I overheat, or over work the torque converter ?
Why does factory lock up torque converter in 3rd ?

( 4L60e behind 4.8L )

 

i never locked in 3rd, but i like a really low lock up rpm in 4th. typically between 45 and 50 which is low for most people. at WOT some people see time improvements by locking. i never did but every combo likes something diferetn.

 

Just have it unlocked for anything over 70-80 % throttle. Don't lock a 60 at WOT with power. It wouldn't be a bad idea to dyno it and calculate the converter slip. With a decent converter you won't see much change other than a couple mph increase.

 

I may have misunderstood his q. They lock it for better efficiency, cooler trans temps, if you tow its very beneficial. Who cares if it's a race car though.

 

Definitely NOT a race car. No dyno close by, all testing is On or OFF road.
Daily driver, 4 wheel drive, 34 inch 10 ply tires.
Set to UN Lock at 60% throttle in 4th.
Always unlocked in 3rd.

 

It's very useful in towing or if you have hills you know you can pull in 3rd locked, rather than 4th unlocked and save a few 100 RPM while maintaining speed.

 

34" 10 ply tires
I really hope you have re-geared the truck.
If not, that's just silly and you're asking for trouble.

Stock tq converter? If so, leaving it unlocked in 3rd is fine. Will likely extend the life of the converter clutch.
You will however generate more heat and need a better trans cooler to deal with that heat.

Do not ever lock anything with heavy throttle using anything other than a triple disc tq converter.

 

4.56 gears, 11 pounds manifold pressure..