You need to make sure you don't waste too much time capturing the energy generators.
The intersection from the valley where you start to where you have to pass to get to the ramp must be guarded by several turrets to beat off counterattacks.
I would have at least four or five groups of forces:
5. Dellis and stormtroopers in the armored car.
Advance each group up the ramp, one right after the other. Keep them close so they can defend each other. It probably is a good idea to leave the AT-AA's on the third leg of the ramp. Send the rest of the forces up the ramp and have the AT-ST's take care of the tanks at top. I didn't know if the mobile attillery was available then. I took care of all the defenses at the top before getting dellis up there to stop the drill. I pretty much piled on as many forces as possible because I lost alot on the way up.