Sloppy slip yokes

i have my 70 duster, 360,4speed,8 3/4
Its fun, and scoots along pretty good for a street car i drive around... but i cant get rid of my dam slip yoke vibration

The vibration get noticable around 60mph and gets nothing but worse.... any gear, clutch in, neutral, it dont matter.... at 80-85 its shakin the shifter bad, and im waiting fot the driveshaft to catapult mein the air!!!

So i have replaced the tailshaft extension housing bushing, no change, and the old one still looked new...and i have bought two PTI? Slip yokes from summit racing, and thoz all seemed to be looser than the old 70s mopar yoke.... and vibration was real bad, i could even shake driveshaft and watch the seal move around... i dont kno how it never leaked...
Now im running a spicer 1350 yoke that fits better than any of them yet, but i can still shake the driveshaft and it still shakes the car goin down the highway

Anyone got any ideas? Im stuck??
It be nice if someone made tight fitting slip yokes... if i gotta rebuild this tranny just to put in a better output shaft, im goin with 5 or 6 speed