Fullback and linebacker tips?

OK so I am moving on to varsity football next year because I am going to be a junior I am 15 because I'm young for my grade. I am 6'1" and weight about 180. I don't know my Max in much but my Max bench is about 180 and I'm going to be lifting. In my recent years playing football in fullback we run a full which is the basic qb fb and RB straight back. I did alright in jv playing fb but it was just my first year play that position and I succeeded in throught my weight around going hard and getting a head full of steam. I run like a 5 flat 40 meter dash so I'm not her fast. My coach is telling. Me in varsity I have to be looking for my cutback lanes and other things. I want to try and go to a d2 college for football but I need some tips. Some games I would get 3 td's. A game and usually every extra point going for two so I was quite successful but that was just jv. And on lb I was also successful I had plenty sacks force fumbles and hits. But I was finding my self getting kind of siked out. What I mean is I would be back their and then once they would hand the ball off I would find myself flat footed or else I would overpersue and he would cut back. So I am also looked for tips to prevent that because lb is very complicated And I need help. What drills should I do to increase speed and tips on my position. Thanks!