tranny ghouls when i DONT need them.

[cliffsta]

Well, my transmission might be takin a turn for the worse. It's started leakin ATF very bad, everywhere i park for more than 10 hours there is a nice sized puddle of it, and at my normal spot here at home, it looks like the wrekc of the Exxon Valdez. I haven't checked it in a week or two, cause i never really noticed it was all comin at once (i always park in one spot so there is a big puddle, but i just noticed the "new" spots)
It's also getting real bad about not going into drive. Like backing up down the driveway and putting it into drive, it wont go, or it will start to roll forward barely, giving it the gas has no effect, and finally it LUMPS over into drive. Used to only do it once when first going, now it does it consistantly until the truck reaches operating temp.
I gotta go get gas and when i get back ima check the ATF level, but are there any thoughts on how to stop the leak? My dad said he thinks its comin out the back, as he and my uncle changed the rear mains (if that applies or not, don't get us lying) and it doesn't leak oil. Also, is it just the modulator sticking that won't let it go into drive when it's cold?
And long-term, how much generally does a tranny rebuild cost, or at least some solid maintenace?
I know thats a bunch of vague ?s and its kinda long, but i'd rather learn now then, well, when i'm staring at a busted TH350C at a tranny shop...
Thanks guys and gals,
Cliff