Driveline vibration?

Ok here is the story. I bought a real nice all original 1990 Ram 150 2wd club cab, 318, 4speed. Well I put a new set of Goodyear Wrangler tires on it and took it for my first drive and it had a bad driveline vibration between 35-60 and then it gets less obvious. I pulled the 2 piece drive shaft out and though the u-joints seemed OK I replaced the three joints. The carrier bearing felt smooth so i didn't replace it. The trans is a cast iron granny 4sd. I noticed the yoke on the trans was loose so i tightened the nut. The 9 1/4 3.21 sg rear felt a little rough when you turned the yoke so I tore it down and replaced all the bearings in it. When I drove it again it is some what better but still has the vibration? Any ideas?