i am not that familiar with gold rams, and my comments here are from my experience with true (german blue) rams, but i dont see what they shouldn't apply
the third spine on a male mature ram will be elongated...
but the more reliable method IMO is looking at the top of the tail end of the dorsal fin. its more pointed on a male and rounded on a female. its not that obvious unless you have both to make a comparison, and is often not pronounced on younger fish. really it just takes a trained eye. as with most things in life, theres no substitute for experience.
search 'apistogamma' on a good search engine for more complete information
if you come across a hit containing 'Z Man', there's a better source than me
i wouldn't rule out a territory battle though. rams are tough little suckers, and the established one would have a distinct advantage due to stress caused by a change of conditions.
rams tend to be rather finicky to pH and water hardness, but if you have a healthy one, beats me? maybe go back to the store where you got that one and inquire if they are of the same source.
on acclimating.. i have a tip..... instead of actively adding water, after enough time to equilize the temp, poke a VERY small hole in the bag. make it a little larger in a half hour or so, and so on and so on. this is how i acclimate all my new additions. sometimes i take 6 hours if i'm particularly concerned, and eventually let the fish find their own way out. sometimes this helps in other ways too, like letting other fish get used to the idea
oh yea, rearrange the tank on addition too... helps equalize the terratory thing
other than that, i'm afraid i can be of little more help, other than sympathy. i went through a phase of mysterious ram losses, and am still at a loss
this may seem cocky, but reread this a couple of times. i often miss stuff when i read.
hope this helps you.
good luck
eric
edit: brain fart.... rams are genus Microgeophagus, not Apistogamma
