2012 Chevy Silverado 1500 new differential

[branedge]

My son blew the rear end out of his truck so we replaced the 3:42 with a 3:73. Afterwards it wouldn't shift into 2nd (seems to drop out of gear). We were told gears being out of sync was the issue. So he bought the T2 platinum so we could change the gear ratio.

We've done this but not it shifting extremely hard and at very high rpms. All we did was modify the default tune from 3:42 to 3:73 is there something we're missing?

[branedge]

so i just discovered that my engine vin does not match my transmission vin...could this be the cause of some of my issues? and i have no idea what happened, used truck, it was fine until the diff blew.

[mikel]

any codes present?

[branedge]

No codes, which is driving me crazy

[mikel]

disconnect the battery for a few minutes, drain voltage, then reconnect and see if its better.