I think he's lost some of his explosiveness. Not that much, but some. We all get old.
There comes a point were you can't go all out all the time and have the same explosiveness in the 4th quarter/2nd half as you did in the 1st quarter/1st half.
Also when you sit and come back in, age and tired legs plays a factor in you getting warmed up again.
I think that lebron is still getting decent lift at the rim. He's just missing a lot of easy layups this year. The last couple of seasons he's been a beast a finishing with contact, even with his left hand. This year, he's not finishing at the rim like he normal does.
I think it's more mental than anything in regards to finishing close to the basket. All I know is he better get it together come playoff time. Also he and wade need improve their FT shooting.