Going from being primarily a 400 runner to an 800 runner and I want to run sub-2:00

Well, you sort of already answered your own question. You said you finally have a dedicated mid-d coach. Trust his training that he will get you to where you need to be.

From what you've provided, you clearly lack endurance. 54 is fast enough speed to go sub 2. I'd make sure that you're getting in good mileage on other days (don't sacrifice recovery, though, just to get miles) and a nice long run if you can get it in every week.

If you're coach is good you'll have a mix of 1600/3200 pace workouts, and then later on a lot of race specific 800 workouts, plus 10k/5k/threshold stuff throughout to help get that strength side up to allow you to finish that second lap.

What are is your 400 split on the 800?

I see many former 400m runners who try the 800 go out way too fast in the 800 and tie up

Along with endurance. You should learn some pacing.

Also race a good number of 800s.

My 400 splits in my 800 PR last year were: 1st lap: .58 second lap: 1:07

I actually have been getting in mileage this year. Last year I never went on any runs longer than a mile and since about mid-January I've built up a pretty good base of 4 miles.

I'm sure you're right about it because the 2 guys who I've been running with (2 best distance runners on the team) and the distance coach have told me that I'm going to be surprised at my times once I get in competition

Hans Yolo wrote:

Well, you sort of already answered your own question. You said you finally have a dedicated mid-d coach. Trust his training that he will get you to where you need to be.

From what you've provided, you clearly lack endurance. 54 is fast enough speed to go sub 2.

Only with a lot of training.

My advice - whatever longer slower training you're doing, don't let your 400 time deteriorate. Don't ignore the speed work you need to run a fast 400.