You've mentioned an interesting point. In nets you say you follow through whereas on the pitch you don't, which means two things.
a. You aren't practising what you bowl in the middle in nets.
b. You are thinking about your delivery and follow through too much as you bowl.
The principal of clearing the mind applies to both bowler and batsman. Decide on the ball you are going to bowl at the start of your run up, then run in and bowl it as though you are in the nets. Don't worry about where you put yourself, just focus on where you are going to pitch it throughout your run up and deliver the ball. That's all you can do. It's really hard to do but will benefit you.
The second point I'd make is that, coming off grass without netting, you will always tend to appear slower. There isn't the zoom effect of nets to help and the surface at this time of year is definitely slower, regardless of how good a track it is, especially if you hit the ground quite hard with the ball.