'06 tranny issue

[SmokeEater]

Hey guys, I bought an '06 Tundra 4x4 in December with 19k miles on it. Its at 25k and for the past 2k or so miles I've been having two problems.

1st: When I come to a stop, the truck lurches forward as if I have been bumped from behind. It happens when I am slowing (0-5mph) or am at a dead stop. It feels as if the truck is trying to overpower the brakes for a moment. There have been a couple times where instead of a single lurch, it has been several as the transmission rapidly downshifts through the gears leaving me to believe it has something to do with the tranny not disengaging as it downshifts and I come to a stop. However I have no idea what that might be... all my tranny experience is with manuals. This is my first auto.

2nd: Occasionally, the tranny wont upshift like it should. I'll be cruising along with no load on the motor at 3300rpms in 4th gear and it wont shift to 5th. I know it will do that automatically until it achieves operating temp but I've had it happen at the end of a 250 mile trip.

I took it in under warranty but the dealership has given me the runaround... I was told that since it isnt throwing any codes, theres nothing wrong and I'm imagining the problem. So has anybody had this problem or have any ideas what it might be??

Thanks!