I've had issues with the 5 bank and TNT bank as well, but simply running a cloth through the opto "groove" fixed the issue.
ACDC is notorious for little connectors coming loose after a number of plays. Maybe try to squeeze them all tight and test again?

You'll also need to adjust the under-playfield targets from time to time.
When you do this, make sure that as you lift the playfield up, that the ball in the lower playfield rolls around to the back, not touching the targets. If you yank the targets, it can be annoying to put them back in with the ball in the way.

These are on my list of things to order.
http://mezelmods.com/products/stern-target-splints

That's my understanding, though I'll probably grab a few extra for the standup targets beside each ramp. They don't move much, but these are cheap so why not?