I've been promotable for 6 years, SSD 1-3 is complete, and still can not get an 88M ALC slot. What do I do?

Start with a visit to you BN CSM, Ask him(her) what else do I need to do? Then do it. Ask How can I get a slot? I want this.
If you get a slot, mission accomplished if not...

Are you fit, like really fit?
Are you smart, motivated, self disciplined, NEVER quit attitude?
If you are positive nothing but death or the IRS would keep you from finishing a school house ALC (and death would likley still not have the advantage)

Make a challenge through your CSM to SMA Dailey.. Ask him.. .. How many No show the 88M ALC class date assigned? ..
SMA you get me a slot, I will be there.
SMA, how many show up unable to complete the simplest inprocessing APFT? I will pass....period.
How many are released or refused entrance due to overweight ?
How many are released for disciplinary reasons, DUI, Drugs, Adultery or arrest?
How many fail academically?
How many barely pass?
How many complete ALC and then get out inside of 12 months essentially wasting a ALC spot?
SMA Dailey I will be at the schoolhouse on time, in uniform, prepared, I will pass the APFT and Height & Weight screening. I will not do anything to discredit myself, my unit, the Army. I will complete the course with top honors to the best of my ability and I intended to remain in the service of my country using the skills I have earned to benefit the units mission.
I ask of you SMA Dailey ... please dont waste another 88M ALC slot on a Service Member that is not willing and able to earn it... the schoolhouse can call me on thursday of a no show open slot and I'll be there as fast as an airplane ticket can be processed and get me there.

SGT(P) (Join to see) But be cautioned, you will have set yourself up for a monumental failure if you can not achieve the statements of ability you profess to him.. If you can not walk the walk, keep working the system, it'll happen when it happens.

What you may find is the BN, BDE, DIV, III Corps CSM will accept your challenge, make a call and you will find yourself on an airplane going to the next ALC.... Because every leader likes a professional, confident CAPABLE fighter, willing to throw it all out there on the line for what they believe in, for the betterment of the Army. As the 1CD DIV G3 SGM and the guy in charge of schools.......I can tell you there are ways for a DIV and higher CSM to get you a slot.... but no one will stick thier professional credit on the line for a maybe, for a probable

Start with your Schools NCO, see if the OML is up to date and where you fall in at. If you're at the top, but aren't getting a slot, then you need to get with the 1SG so he can find out why, out do he can set you up a meeting with the CSM to find out why you aren't being slotted for ALC. Somewhere in that, the problem should get fixed. If not, you can always email the Schools manager at HRC. It might be your place on the OML once it gets to that level. I do know from experience that you're in a large MOS. Hopefully, they can get you a slot at Lee, or in a nearby MTT, if one is available. Best of luck!

If you have gone through you COC then I would go higher to Batallion the Brigade CSMs or start looking for another unit.