24 years old, overpay on “high” interest mortgage or max Roth IRA?

I’ll try to add as much context as possible. I’m 24 years old and enlisted in the National Guard. I purchased a home about 7 months ago on a VA loan with $0 down and rolled the VA funding fee into the loan (no PMI, but a couple extra thousand on the mortgage). I have a 3-4 month emergency fund, I have no other debt, two reliable cars that are used for different and justifiable purposes, a reasonable income that has recently been supplemented by a second job, and a healthy 401k. I have read the Wiki and I guess the overall question is whether or not my mortgage would be considered high enough interest to pay down before investing more.

Mortgage -

Home valued at $319,000

Owe $321,000 at 6.624%

I am paying an extra $150/month as a buffer but worried it’s not enough or that money should be going elsewhere.

401k -

$138,000 invested in lifecycle funds targeted at the year 2055 (I’m not active enough or knowledgeable enough to manage these myself but it’s better me significant gains the last few years)

I contribute 12% of my income which is just under half of the max contribution limit, in addition to a 4% employer match and an additional $1,100 a month from an employer sponsored health and wellness fund that would otherwise be paying for health insurance if I wasn’t covered by TriCare. This totals about $26,000/year

Roth IRA -

A little over $8,000 invested. Minimal contributions the last few years, throwing money at my 401k and living expenses.

This has been what I could afford for a long time.

As I mentioned, I have a little bit of supplemental income now; about an extra $2,000/month.

My question is whether the 6.624% mortgage rate and the fact that I’m underwater on the house is grounds for overpaying on the mortgage or maxing out my IRA first, or contributing more to my 401k.

Worried about the housing market and the fact that I have 0 equity in the house as it is. Advice is appreciated.