trans question

ok guys im thinking its trans issues that I got just want to see if anyone else had this problem, I have a 71 dart swinger with a 340 that is fresh 1000 miles on it may be and a 727 trans with the same, now when I first get the car out and drive down the road I feel like the brakes are being applied for a second or two then its releases and it does this for a bit then when cars warm its not there, now Ive been doing some testing to see if its with motor or what ever well if jump on the gas and let the car coast I can still feel it, so I thought the brake may be hanging up in the rear or something checked them out all good, and I also noticed if im cruising and its doing it and if I give it a little more gas it goes away until the speed flattens out so I don't think its a trans issue could it be a torque converter issue any help would be great