What should I expect to learn or should prepare myself for when reclassing to 88H as an E6?

While I have no knowledge of the course nor MOS...other than what Google tells me.....going in as a SSG MOS-T, you will more than likely be granted more freedoms than the IETs you may find yourself training with if you are put in a training company that has IETs. All I can say about this is to stay the Hell away from the IETs outside of POI time if you're in that mix of a company. As for your day to day, this will (and this includes what I found on ArmyWriter) "MOSC 88H3O Cargo Specialist: Plans work schedules for terminal operations, airfield arrival/departure control groups, (to include passengers) and container/trailer transfer points; utilizes stowage plans, aircraft load plans and other cargo handling forms; issues materiel handling equipment, nets, slings, ropes, cables, wire, rope and other cargo operations gear; enforces safety practices; prepares, consolidates, and reviews administrative, personnel, and technical reports covering unit activities." To me, this sounds like flight line work. Of course, you could also find yourself in the BN S4, or even a warehouse.

The issue you're going to immediately face is that you will be behind the power curve and will have to catch up most rikky tik IOT catch up to your peers.

I would add somethign to what others have said, see if there are Correspondence Courses and take them. It will give you an understanding of the field. See if there are any books (TM's, Pub's, FM's) on the subject and get familiar with them. I see people refer to rope skills. When I went through Paramedic School years ago, we used some 550 cord and some cheapo Dollar store mini carabiners to go over how to complete knots, how to set up sling loads (patients not equipment), much of which I think may transfer to this field. Search your motor pool to see if they have ratchet straps and or chain tie downs and practice tiedown something so you can be familiar with how they work. My $0.02