I have a 15K mi 4L60E in my 55 Chev, with the 6.0.. Slightly modded. [Engine/trans is from an 05 H2].
I am in the process of tuning and find that 4th gear is "locked out" @ WOT. [255mph/8000+ rpm].
The trans has been inspected, the sun shell welded, and some bushings replaced w/ better pieces. It has the 5 gear planet and the Vette servo.
No shift kit.
The converter is a Trailblazer unit for some added stall speed.

Is it not a good idea to change the tune so 4th gear will apply at WOT?
More line psi?? How much?
Shorter shift times? How much? [It feels too soft on part throttle shifts].

TIA

 

that is perfectly normal for a 4l60e. i dont think they are designed to go into 4th at WOT same with a 700r4

 

THANKS!
I'll just leave it alone!!

 

I had an '84 TA. There was a cheap kit that would allow more throttle or WOT in 4th. I got mine from one of the popular racing parts catalogs years ago. I don't know if it's still available.