Most likely you will find a big improvement (less wobble) with a little more distance... I believe that when you begin riding bents you tend to tense up a little bit and this exagerates steering movement.
With some more distance you will relax and things should smooth out, this does assume that the wobble isn't caused by a mechanical problem or a poorly designed bike... since you said you tried several Rans recumbents, I doubt it's a problem with the bike.
I find looking well ahead seems to help with keeping things straight.
Get some more miles in... relax and enjoy.
A friend would bail you out of jail... A good friend sits there beside you and says "Damn that was fun"
Hills can be a problem on a bent as you can't use body weight to increase the torque. You learn very early to downshift when coming to any stop. The wobble factor is always greater with bent, but several hundred miles of riding will reduce it to near DF range, except when starting up hills! It is a good idea to use BMX type platform pedals for 3-400miles until bike handling becomes natural and then shift to clipless. BMX pedals are cheap. One other thing about Rans type bikes (not particular to Rans but any with the "chipmunk steering position") is that the harder you grip the bar the more the bike wobbles. A very lite touch is all that is needed. Keep those fingers loose. Steve