the AT1545 and the AT545 share a bunch of parts, service bulletins, tech info. i beleive its just an inclusive (both series) sticker as to the driving ranges.
find the longest steepest hill you can and try these 2 tests.
floor it on the way up - keep the rpms pegged to the max, then look and see if you slow down? if you do and the rpms stay max, its not locked up.
on the way down the hill, go fast. get rolling fast and take you foot off the pedal. do you slow down, does engine braking kick in, or do you just keep rolling downhill? the 545 can engine brake a bit, going slow, but fast with lots of mass quickly overcomes the clutch pressures, the trans makes noises like its fallling apart and you go screaming down the hill.
down a steep grade is scary in a 545 because it doesnt engine brake very well or not at all. thats the lockup's function.
the uphill is probably the safest way to tell. imo thats what kills the 545. slippage going up a hill.
if you have lockup, you would have a 1545. thats the difference, as far as i can tell.