Mower was running great and when I stopped engine it backfired and from that point on it lacked power and is backfiring

1) was the backfire through the intake or exhaust?

2) when you say still backfiring since for you mean while it is still running or just when you shut it off?

Seems to put and sputter under power. I don't know if it is intake or exhaust

It sounds like you may have a valve issue. Either burned or stuck open for some reason. You need to run a compression check to be sure and also check your spark plugs.