2ksleeper

I have a problem that only happens during a 2nd to 1st shift downshift other than that the transmition shifts fine. After the downshift the rpms keep climbing past shift point set in pcm & it bounces off the rev limiter 3 times before it finally shifts. After it happens I checked my predator handheld & the computer threw the following coded in the DTC NOT RAN AT SCC: p0742, p0751, Po756. My truck is a 2000 silverado w/5.3 whipple supercharger @8psi+alki injection, headers, intake, transgo shift kit, billet main + overdrive servos, cleaned cats, o2 simms. The problem was noticed after cleaning the cats out. All the following thing were done to try to fix problem to no evail: unload the predator tune & install the hypertech tune, install shift kit & replaced the valve body plate, replaced shift solenoid "a" & "b", and cleaned the MAF. Any help will be appreciated.