I havent noticed any real problems with the drieshafts. I think I have a loose pinion in the rear though. I havent gotten around to checking it.
While my rear shaft was getting lengthened, I drove around on my front shaft, which is 1/2 inch short. The result was fairly noisy as the ship yoke had some play perpendicular to the shaft. This would make noise when driving along at 30 mp/h or more and under no load. If I had load, no noise.
I suspect that you will have a similar issue in the rear shaft. I'd be interested in hearing how much overlap you have in both your front and rear slip yokes.