hmmm. i also need a new torque converter.
theres a little shutter when shifting down to third. i did lots of research looking for the problem, and troubleshooting came down to... tap/hold the brake when it begins to shift down. if there is no shutter, then the torque converter needs to go.
just sharing a little learning experience

 

You should try if you have a good budget to get a used 5.7L I got one amd its made a difference

 

What u need my g.... Is a tune street tune....headers long tube to be exact....228/228 cam... Shift kit.... U tune after u have installed all the mods then u should easily be running low 12"s in a qrt..... That's what I'm running in my single cab 2012 2dr 5.3 I yank on boys all day and all this I spent maybe 1200 bucks over a period of 6 months and my **** is fast I'm from Houston Texas and truck scene out here is outrageous I'm sure you've heard

 

All I can tell you is buy some insurance and a casket, cause sooner or later if you keep going faster your luck will run out, and you will need both!!!!!!