Is anyone familiar with the Marine Corps PSEP program?

I've served 9.5 years in both the active and reserve components of the Marines.
Currently in the Air Force right now and looking to go back

SrA (Join to see) - Okay, I'm on target.  It may prove problematic, age, and returning as a SSgt.  
I'm assuming that you have 10-13 years combined res/active service, USAF and USMC? 
If you come back as anything less than a SSgt, you'll be putting yourself way behind the power curve.  Same even applies coming back as a SSgt.  My point is, the first time your package goes before a promotion board, the first question they'll ask is, where the f*ck has this guy been. Even with an adjusted DOR you may not the zone for a while.  You'll be behind your peer group.  Potentially you could see yourself passed over, and unable to re-enlist.  
Never say never, but I would advise going to an RS Hq, and posing the question to them.  

Thanks for your response Gunny. The info goes as follows: I will have as of this Nov. 12 years of Federal Service. As its stands right now I'm sitting at 5 yrs and 3 months of Active Duty time. I have about 4.5-5yrs of Reserve time. I'm currently sitting in the Active Component of the Air Force as an E4, which as you said has put me behind my peers. This transition with the Air Force has been absolutely atrocious and I'm actively in the process getting a DD368 signed by my command. What I'm trying to understand is do I have the ability using my PME certs. and having achieved the pay grade of E6 in the Marines, have the ability to enlist into the Army as an E6 or E5 through a grade determination waiver? I have a prior service accessions rep. at US Army Recruiting Command tell me that because I signed a contract with Air Force stating E4 that I apparently waived my rank in the Marines away. He's saying that the Army doesnt promote or demote prior service applicants. My arguement to him was that I wouldnt be getting promoted seeing as I've already achieved rank to E6 through my Marine Corps experience. He seemed uncertain at that point and referred me to promotions at US Army Human Resources Command.

What do you mean by RS HQ?

SrA (Join to see) - RS HQ = Recruiting Station Headquarters. Here's my take.... you left the Marine Corps as a SSgt and accepted a lesser grade in the Air Force, your current grade. A conditional release would reflect your current grade and assignment. In transitioning to the Army they may take into account your prior service in both branches and enlist you in an appropriate grade. I may well be wrong, but I don't see the Corps re-enlisting you as a SSgt, hence my advice to seek guidance from a RS, or even HQMC.
Best case scenario is that you re-enter as a SSgt, but this would be bring certain risks.
1). A long wait for promotion, or being passed over. The latter having an affect on your ability to re-enlist.
2). Being re-enlisted at a lesser grade, Sgt/Cpl, having the same affects as above.
Advise I'd give; seriously review your current situation. Are there changes, Lateral Move, PCS, etc..., you can make in the Air Force? If you determine that changing Branches is your best option pursue it vigorously, but realize the risks that the change could bring.