leave blower question

OK SO< I know this is an ATV site, but motors are motors LOL
I bought a Ryobi 43 cc 2 stroke backpack blower last November, ran good then started to run like crap, every time I shut the thing off, it would run like crap for 5 minutes then run fine
after a few weeks of this I took it back and they gave me a new one
last few days been using it again, and having same issues

the issue’;s being when it starts fine cold, runs fine hot, untill I shut it off, add fuel or just shut it off
I get a LOT of air pressure releasing every time I open the fill cap, ?? actually some times will NOT start unless I open the cap to let air in.pressure out!
NOW< it will start in 2 pulls after I open the cap, BUT will run like crap, idle/rev’s up and down at will, will bog or rev when applying throttle, OR stall if I give it too much, then and ONLY after I ran it for a while, it will run funny every time I tild the motor, like its starves for fuel then gets too much, or the likes
BUT after running for 5 minutes it great again!

here is what I have tried! and sure are right

fuel is good and mixed right
spark plug, teied new one’s and old obne’s look fine?? doesn’t change anything at all
air filter is clean
treied running with gas cap on and off when it acts up, make s NO difference!?
again this is my second one with same issue’s(has a 2 yr warranty, 1+ left LOL)
when it runs it runs great
only have issuesd when I shut it off and then for 5 minutes after I start it back up, and will do so, hot or almost cold!(running for just 5 minutes or so)

any idea’s

other than live with it??