94 Silverado Rear End Noise

Your engine RPM issue is NOT related to the rearend noise, if it were, your truck would not move at all. I would say that the lock-up function of your torque converter is no longer working (assuming its an automatic). The whining noise you're hearing when you accellerate is more than likely the pinion bearings. But it has been my esperience with these rearends, that when they get to this point, with that amount of miles on them, every bearing and probably the ring and pinion gear will need to be replaced. You might be better off to start looking on ebay for an entire axle assy. Out of a used lower mileage wreck. It'd be much cheaper. In the mean time, always remember to CHANGE your rear axle fluid at least every 40,000 miles. If you use your truck for heavy hauling or pulling a heavy trailer all the time, change it every 20,000 miles. Good luck.