Messed Up Transmission

[97vtec]

i've got a 77 bronco with a c-4 tranny. I got this wild urge to drain the fluid drop the pan and change the filter since it had never been changed before. well when I did this I added a drain plug to the bottom of the pan. I put everything back together and started putting fluid back in the pan except (I did not know this) when you put the fluid back the motor is supposed to be runningin park. So 4 quarts drained out and I put 4 quarts back in but not while the bronco was running. I took it for a test run and it shifted kind of before it normally did and it wasn't kicking down like it was supposed to. So I turned around and was coming back home when I noticed white smoke coming out of the back in my rear view mirror. so in stead of stopping I tried to make it that last mile and 1/2. I got home fine but it left a trail of tranny fluid in the driveway. so I let the bronco cool for a few hours drained the fluid and put fresh back in except with it running this time. well I took it out for another test drive and when it stops it doesn't kick down into 1st it tries to take off in 2nd, and when I brought it back for a second time the tranny fluid was still leaking around the sides where the oil cooler lines go into it. I talked to one mecanic that said when you over flow transmissions like that, they are suppose to have an overflow tube that blows excess fluid out(but he works on newer foregein cars). Did I **** the tranny buy tring to drain the fluid? Did I mess it up so bad that I need another c-4? help please any info is good info