1976 Ford F-250 Drive train

Please help me I am stumped big time. I just bought this truck and 2nd gear makes noise, but in 3rd and 4rth gear it sounds like trans. Is falling apart. Guy told me it was throwout bearing. Anyway went ahead and put all clutch parts in it and while I was at it had trans checked and was great gears all good new seals put in. Also prior to that I took two piece driveline and had it balanced and it was o.K. And new center support bearing, its like new. Everything was put back in today by my son and I, I'm not rich so I try to do my own labor, plus I love it. Well I am BUMMED the same darn noise is there like we did'nt do anything. Now I dont know what to do. Engine runs great no noise from it, it, s a 390. Trying to listen under the truck the noise travels everywere. Could this be the rear end? ONLY noisey when you accelerate, doesnt matter what speed your doing noise stops as soon as you take foot off gas, step on gas again it sounds like its going to blowup. Clunking banging noise especially in 3rd and 4th and not as noisey in 2nd. Remember trans o.K new clutch set, driveline done PLEASE HELP I would be so greatful. THANKS, Joanie