06 infiniti G35 transmission question

Hi, I recently purchased an 06 Infiniti G35 automatic. It has been great, but noticed about a month ago that the engine starts to lug around 40-45 mph after I have been driving it for about 20 minutes. What I have been doing is removing my foot from the gas and then accelerating ? Has anyone experienced this & do you think exchanging the transmission fluid will alleviate this issue…? Thanks!