tranny/driveline help needed

[rebreath]

some history first...
Bought the car in may.had a bad center bearing,still driveable.drove slowly home from NJ to pittsburgh.did fine until last fiftyish miles,when vibration would not stop.so I had it towed the last bit home.changed center(support)bearing and shortly after both flex joints.seemed to fix all probs.drove to and from maine(i tend towards the 80 mark on the highway),problem free.to and from rochester,no prob.countless trips around the burgh(I love to fish) and surrounding area.again,no prob.had to go to syracuse last week and suddenly there is a problem.
Tooling along at about 75-80 when suddenly vibration similar to center bearing failure occurs.to shoulder and under immediately.all was tight and snug.slight play in driveshaft,but overall snug it seemed.back out on highway again,slower this time(50-60) about ten minutes later noise,only this time accompanied by a rhythmic metallic sound also.to shoulder and under again.all is same.parked car-rented car-to and from syracuse.then back to where car was stuck(wilkes-barre,pa).paid a shop to lift so i could get a better look,here is what three pairs of eyes saw.back left control arm bushing is loose(grab wheel at 3 and 9 and wheel moves about 3/8 inch or so.driveshat seemed solid and snug,output shaft on tranny seemed snug(no play)all mount bolts were wrench checked and were tight.decided to drive her home,drove 45 for about 6 hours and suddenly the thumping is back.shoulder,under,check all the same.back out and 10 mins or so back with metallic sound accompaniment.rent room for night.wake up next day,out to car,start her up,drive a bit.no noises.back to highway and make it back to pittsburgh without further event.any thoughts?what does the intermittance indicate?I have not had the car back up to any real speed since it happened last week.could the initial drive from jersey with a bad bearing have done lasting damage to something?I did not exceed 45 the whole way.It did not vibrate the whole time,only when slowing or going over 45mph.several thousand miles since then without any probs.I am gonna pull the shaft and have it checked at driveshaft shop,pondering chasing a good used tranny down if needed (hope not).thanks for your insights....