6R140 The 3-4 shift goes into “neutral” for a couple seconds. Started with PDI tunes, heard so many positive things about GDP I bought their tunes, both TCMs get same results. Changed/flush added a BD Diesel pressure enhancer, the other shifts greatly improved. But not the 3-4. I tow 12,000lbs weekly and when I’m towing I “M” shift the gears, the 3-4 takes a good 3 seconds before I can resume throttle. No codes. 60,000miles. Took it to the transmission shop that I’ve used and trust, He doesn’t have any answers without remove and rebuild but thinks it’s a blown seal. Once the shift completes there is no slippage. I've never moved the SOTF off of 0HP, good grief these things have almost 1000fp torque.