Shift flare / tranny slipping?

Drove my truck from Florida to Virginia and the tranny like to stay in 4th buring a crap load of fuel. Constant downshifting is so annoying to me. I know the bigger tires doesnt help any but never had any issues in my Tundra acting this way.
MPG for a 9hr drive going 75mph

 

Do you have the transmission software update?

 

Yes, at least thats what the service writer told me they did..not 100% definitely sure if it was done being it was been closed doors.

 

You weren't driving it in S4 were you?

 

No...definitely in "D"...on small incline..it loves to downshift and when I let off the throttle, it feels slows down drastically as if its slightly braking.

 

Mine does the same thing