2010 5.3l 6spd wierd downshift

[Stevil Knievel]

I've got a 2010 5.3l 6spd Silverado 1500 that I had a local shop tune and now does this quirky thing when it downshifts on acceleration. More noticeable at higher speeds, but what happens is my tach instantly jumps up then is pulled back about 300rpm then starts to pull. So say I'm cruising at 110km/hr @ 1900rpm; if I floor it, the tach jumps to 4000rpm then a fraction of a second later will drop to 3600rmp then pull. You can feel this surge when you drive. The guy removed the TM and turned up the line pressure and shortened shift times, and unlocked the torque converter. Any idea's what might be causing this? It's almost like it's slipping but he says it's not?

Thanks
Steve

[ScarabEpic22]

Sounds like the converter unlocking then the trans is downshifting. Need to see a log of whats going on with trans PIDs selected.

[Stevil Knievel]

He thought so too, so he doesnt have it locking up.