2005 4Runner intermittent problem- engine sluggish

Thanks for the welcome. I recently changed the oil in our 4Runner with Amsoil about 1000 miles ago in November. I ran an engine flush through it first...good idea bad idea I don't know. However, here recently I've noticed that my Runner doesn't seem as peppy at times. I can go turn it on to go somewhere and it responds quite nicely with just a little touch to the accelerator. I can shut it off, go into the store, come back in 15 mins or less, engine still up to temp, take off and it's a little sluggish not responding the same. Sounds a little differently too. Not really bad sounding. Idles great. No engine codes. Had a friendhook up a hand held computer diagnostic...nothing.
It can do just the opposite...seems sluggish at the start, gets up to temp after just a few miles...no change. Still has decent power, but you have to push accelerator down a little further to down shift to really go. Turn it off, start it back up, and responds normally. Just purchased Runner in May 2017 from dealership with 152k on it. Great condition. Tune up, not sure?

 

do you know what maintenance has been done on it? are the spark plugs in good condition. if theres a fouled plug temp can play a role there as well. Not sure if that would solve your issues but it could be a starting point

 

Please describe the engine flush you performed.