Have it looked at ...but honestly sounds about normal to me. its natural to hold a gear longer while going uphill...if it didnt it would upshift then have to down shift again to maintain speed based on your throttle input. Why does it happen only on take off's on a hill...well if you are already rolling and go up hill its easier to maintain speed...you may not even be noticing the slight downshift.
Jeep #3.. 2012 JKU Sahara, Deep Cherry Crystal Red with body color top and fenders, automatic, 3.21's with limited slip.
2010 Mustang Gt 5spd, 3.73's, SLP loudmouth axle back,Roush CAI, factory 19's,leather and glass roof.