I'm with shmegeggie and longjohn on the idea of it being the (lack of) reflections from the floor.

If there's some way you can try setting up the kit on a more reflective surface....not necessarily a hard floor, but maybe a thinner rug or carpet with lower pile?

The real question is: when you hold the drum in one hand and hit it, on the rug, what does it sound like? I've experimented with 4 snare stands and some were magic, some actually made it worse. RIMS really are the way to go. However, my last vintage Ludwig floor tom was almost a 16th higher at one side of the shell than the other. I sold that kit because of the toms. You can be lucky though - the good ones are out there.

I'm going to try the foam on the snare stand idea. Also, I'm really curious about the straight legs on the floor tom deadening things.

Lot of talk about stands and mounts. But did I miss what heads and tuning you have on the drums? Seems to me that's the first step

re: floor tom - make sure it's not the position in the room!

I recently added a 16" tom as 2nd floor tom, and tried to make it fit the rest of the kit. The sustain was ok but on the short side, I blamed it on the higher tuning I favor.

Then I put the drum from close to the wall into the middle of my practice room, and the sustain increased considerably. Something about the wall proximity seems to stifle the vibration.

I'm running Ambassadors at medium-high tuning with the resonant head a minor third higher than the batter. I've tried same tuning both heads, higher tunings, lower tunings, etc. Incidentally, it doesn't matter where the drum is: upstairs, downstairs, middle of room, near wall, it still is dead unless I hold it over a smooth, flat surface like a table top. Now the floor tom does sound better in a room with a lower ceiling. Go figure.

Edit: Diplomats on the resonant head.

Glad to hear you aren't using Hydrolics :)

Well I would say if you are getting the sound you want over hard surfaces and not getting it over absorptive surfaces ... play over hard surfaces (Dr, it hurts when I do this). In this case there's nothing wrong except your expectations. Setup over a sheet of plywood.

Do you get more sustain if you hold the drum up in the air by grabbing the rim in one small place?

Lower ceiling would change the sound by giving you quicker early reflections, so that's understandable. Near hard walls and especially in the corner of hard wall surfaces should do similar.

Nope. I used hydraulics 30 years ago. No good for jazz/big band.

I get fabulous sustain holding by one hand over a table. The drum sounds incredible. The second I move it over the floor it stops. No sustain whatsoever. Uncanny! I guess I'm looking for a relatively simple solution. I don't want to drag a piece of plywood to every gig.

I don't think it's a case of the drum being bad ... but on the fact that when you play near a reflector you are getting a extra boost because of the reflections. Think of it in the way that your hearing improves when you hold your hand up to your ear or singing in the shower.

Sometimes my drums sound exceptionally good is some rooms and then not so good in others. But it is the room acoustics not the drums themselves that is the biggest contributor to the sound as the drums don't essentially change.

Here's a cheap fix for the floor tom:

Go to a hobby or craft store (like Hobby Lobby) and get some 2" thick foam (they come precut in several sizes, the 14" x 14" square size will be cheapest and plenty of foam to use). Make sure to get 2" thick foam; the 1" thick compresses to easily and won't work. Cut the foam into 2" x 2" squares and place one square under each floor tom leg. Works like magic! The floor tom is actually "floating" on the foam rather than sitting on the floor. Also, the foam squares are easy and light to throw in your stick bag. And with a 14" x 14" square piece of foam for about $5, you have enough to do multiple floor toms! Also works under bass drum legs too! Best of all, they are inconspicuous, to keep the classic look of your kit.

As for the rack tom, I've been told these work great:

http://www.gaugerpercussion.com/flex-frametrade-snare-stand-isolation-system.html

It's basically a suspension mount for a drum without a mount, if that makes sense. Also makes it fit into the snare basket easier too.