In response to the call for ideas tha tmight help act 3, I just had one. It's a bit rough and I haven't looked at all the footage it would require, but it sure tightens things up and ramps up the tension.

In a nutshell, here's the idea: Keep the Russians in charge after the ant scene. Make everything Indy does to get inside the temple into something he's doing under pressure from being a captive of the Russians.

The hard part, obviously, is there isn't enough footage to do it perfect. But the impression can be easily created by taking the shots of the russians following those blinking light things and incorporate them into the scenes of the same locations where Indy first reaches them.

This means: Don't let Marion drive the duck over the cliff and help them escape. Cut the waterfalls entirely. It also means the pressure to solve each puzzle makes more sense and the ending is about Indy going into a situation he thinks is bad, but that he's being forced to face -- rather than sort of waltzing into it and then deciding it was a bad idea after the fact.

Anyway, maybe it's too much. But it sure gets at the heart of why that part of the movie drags. The bad guys aren't doing anything and Indy's motivation is vague. Pressure him into it and the scenes make more sense.