I'm curious how you made out, if you SG still worked you could easily tell if the trans was locking or if you were staying in open loop.
As was said, get out on some flat highway (out of the area) and do some testing. There's probably a fuse or something you can pull to force the car to stay in open loop and you could do some runs that way and do some runs the 'stock' way, if they're the same then you're running in open loop.
Also make sure to accelerate as much above speed as you can before you start going up the hill (think about it as if you were bicycling), and definately come back down the hills in neutral (engine off if you can, but if traffic prohibits, neutral should be fine). I've also taken to coasting to a slow speed before I crest the hill and start accelerating down it, like I'll drop down to 45-50 and accelerate in EOC to 55-60 while going down the hill. You might want to leave your engine on to maintain power brakes if your hill is very very steep.