I am thinking it's the torque converter (3600 pro yanke)....the car seems fine on the highway until I stick it into overdrive and hits around 80 kms, it seems to lack power?? Any suggestions?

I also have a sputtering problem ....it doesn't it only now and again, I'm thinking the distributor (still have the stock one).

 

Does the torque converter have the lock up mechanism? if it does not the converter will have to acheive vortex flow in order to keep the car in motion this is done in your case at around 3600 rpm (due to your stall speed) any rpm below that will make the car feel sluggish