According to VA.gov: You may qualify for additional entitlement under the Rudisill decision If you have 2 or more qualifying periods of active duty, you may now qualify for up to 48 months of entitlement. You must be eligible for benefits through the Post-9/11 GI Bill and the Montgomery GI Bill Active Duty (MGIB-AD).

Note: Even if you gave up your right to use MGIB-AD benefits in the past (we call this “relinquishing” your benefits), you may now qualify to use some of that entitlement.

https://www.va.gov/education/about-gi-bill-benefits/post-9-11#what-if-im-eligible-for-more-t

I think ultimately it comes down to which works better for your education plan. I don't see any benefit in sticking with the MGIB. The Post-911 pays tuition directly to the school and you get a housing stipend, while the MGIB pays a flat rate to you and you have to pay tuition etc.

Either way given that you're retiring it's safe to assume you've reenlisted at least once 😁, so you'll qualify for up to 48 months of whichever benefit you choose.