Billy is right. If you can't play it slow and right you will never play it fast. Somebody once told their guitarist in the studio, if you can't get it in 2 takes you can't play it! Sounds about right.

Billy is right about standing as well. If your goal is to play on a stage, any stage, and you will be standing. you better be practicing that as well. It is different. Always use the guitar you will be playing in front of people when you practice as well, of course assuming you have more than one! Most guitarist end up with many, many, many guitars speaking from experience.

There are things right now I cannot play standing up as well as sitting down.

My wife asked if I had seen the dog bowl. I told her I didn't even know he could.