Potsy s5v8

Hi everyone, just a quick one I have myself an s5 with issues lol basically I can start it and the dash lights up like a Xmas tree sounds awful if you try to drive it judders and struggles to change gear if you do get moving and need to slow down it wants to cut out, but next min you can shut it off and start up and it’s fine runs like a dream gear change perfect anyone had or maybe know the issue???? Appreciate the help