Now this is a critique, don't take it personal, take it or leave it. Please realize that I am currently teaching two new ork players to use their orks well, so if I seem harsh; it is not meant that way. Think of an old wise man speaking in hushed tones for your edification.
Looking at your list I see a mixed list that is trying to combine the best of both worlds, which doesn't really work for orks, but you are free to try it out.
First up; trucks. You are wasting points on the extra armor and grots. Most armies these days have some sort of melta in just about every squad, so your trucks will die quick. I rarely have a truck get immobilized, they either get their weapon shot off or have to roll on the ramshackle table. Save some points and drop the armor plates, and instead of grots put boarding planks on them. The ram is almost required gear, allowing you to go through terrain rather than around it, not to mention the +2 for tank shocking, so keep the ram.
Truck boys; change the nob to a PK. As an eldar player I learned that most of the aspect warriors were just wounds for the exarch, i.e. an exarch delivery system. Well, truck boys are kinda the same thing, they are wounds to make sure the nob with PK gets into combat. Plus, having a boarding plank on a truck allows the nob to make his attacks without dismounting, and S9 is better than S7 when killing dreadnoughts and tanks.
The truck boys are the back bone of this army, they are your troop choices as well as your main thrust of attack. The big choppa will not kill most enemy things as AOD mentioned. The PK works, so go with what works.
The kommandoes are a very small squad, at least give them burnas so when they jump on a squad of long fangs/devastators, et al, they have a chance at killing some of them. You will be surprised at how hard it is to get past those pesky 3+ saves. I would say drop the lootas, and beef up the kommandoes if you really want them.
The big mek with SAG; since you have vehicles, I highly recommend the KFF instead. It will keep your trucks alive a little longer until they can deliver the boys, then the trucks are just bonus units to drive around tank shocking things, and otherwise being irritating. The SAG is just a free kill point for your opponent, especially since you intend to set him off by himself.
Keep the SAG if you want, but I recommend that you drop the lootas to get the points to take a KFF big mek.
Lootas; They are a waste of points in this army. They will not deliver the fire support you are seeking. Drop them to get the points for the things mentioned above. Keep them if you must, and you will find that either you lose them all right off the bat, or they are your only survivors. Either way it means you ended up with a "didn't lose" result.
The deffcoptas; two green barons are good. Make sure to run them as two units of one.
Now if this is all your have, then play as you will, but if you can make the changes then I think you will be happier with the results.
Something else to consider; drop the kommandoes and go with got gun batteries. Better BS, and surprisingly effective. Not to mention cheeper in points (if you have the models, and if you are set on being half static and half fast).
Hopefully some of what I have said will help you in your endeavor to become a good ork general.