the uphill rollback suggests the torque converter is starting to go a bit soft. Lots of reasons why this might happen. Any shuddering through the driveline at light throttle, 35-45 mph? The delay in engagement can indicate this. Try this: warm the car up, blip the gas a couple times and shift into drive as the revs come down. Any clunks, clicking or noises? Do a stall speed test. Manually select second and hold the brakes lightly and see how high the revs go when you press the gas fully (Don't do this for more than 5 seconds). If the stall speed is elevated significantly over 2000 rpm, this may indicate a problem.
2014 Premium GT, SGM, Brembo, Auto, Tech, Comfort, etc. GT500s, Steeda UCA, VMP auto tune, 100 shot on BBR tune, best et: 11.38 at 120.85
2012 GT, Candy Red, Brembo, 3.73, Tech, Comfort, etc. Procal tune, Roush upper, UMI LCAs, Steeda red bracket, GT500s, 28X10X16 Hoosier slicks, best et: 11.91 at 115.23 RIP