Transmission Slipping in between shifts

[jacobhill66]

I’m new to the forum and I’m glad I’m here. But I am having issues with my 2014 GMC Sierra 5.3 4x4. The issue is with the 6 speed transmission it slips when it’s changing gears but really only from 1-2 and 2-3 it’s almost like the torque converter isn’t working properly. It won’t happen at WOT but around 35-50% throttle when the truck goes to shift gears the rpms will jump from say 3,000 to 4,000 and sometimes higher. I have had the truck since it had 50k miles on it and have taken very good care of it at 96k miles it had the transmission rebuilt but the only parts the dealer didn’t replace was 1st and second gear. Also they put a remanufactered torque converter in the truck. Since then I have 114k on the truck and have installed a CAI and long tube headers with an off road y-pipe and the truck has custom tunes. And the issue didn’t start occurring until I was pulling my bass boat home getting on the interstate. Also all the mods have been on the truck since 100k so 14,000 miles with the mods and no issues until now. Could it be the converter or something else? Please let me know I need help and also it seems the truck has picked up a bad vibration at highway speeds since the trans started messing up. 

[Lsgun1]

It should have a warranty if it was rebuilt. I'd bring it back to have it looked at.