trans not going into 4th gear even though log says it is?

well i just figured out that my truck hasn't been going into 4th gear at all. It will do 3rd gear tcc locked but that's it. i hooked the scan tool up today and checked it. it says it is in 4th gear and the tcc is locked but if i manually shift it to 3rd the tcc unlocks then locks again and the rpms go back to what they were before.

truck is a 2005 ccsb z71 sierra 5.3, 3.42, 32" tall tires. The only thing done to the truck is a built trans, trailblazer torque converter, and a k&n intake. I've only done trans tuning.. Could the tb stall be causing the truck to not go into 4th gear? I loaded the stock tune back in and it still wont go into 4th gear.

here is the current tune on the truck.

no one has anything that might help me out? im trying to figure out if its in the tune or if its the trans itself.

Had this problem on my 02 TrailBlazer when I botched a shift kit and servo install. The PCM is commanding 4th lockup, however the trans isnt doing it. With your built trans, check the servo installation and if that doesnt do it, probably time for a rebuild...

im trying to help him with this issue also. he is out of town for a few days and wanted me to ask if there is a setting or something in efi live to make it go into 4th? I see you can make it hold 4th thats all i can find. just to make sure its not a tuning issue.

i talked to my trans guy he thinks the servo or accumulator piston maybe the issue also.
any other imput would be great thanks

Grab a laptop and your FlashScan, use the Scan tool, connect to the truck, then click F12 DVTs. Select LS1B PCM, then click activate. Go to the Auto Transmission, and then get to like 50-60mph where it should go into 4th. Click the checkbox, then click Hold 4th. If it shifts, then its a tune problem. If it doesnt, then its a mechanical problem.

Amesome thanks for your help