02 Explorer tranny/driveshaft problems

In the past year and a half, I have had winning noise from the tranny at highway speed. The crown gear and pinions have been replaced separately and together 4 times over that time period. It goes away then returns. There has also been vibrating felt in the driver's seat. Ford has replaced the the driveshaft twice in that same time period. Fortunately, my wife convinced me to buy the best extended warranty so I only paid the $100 deductible 2 times. Last week Ford did the tranny for the 4th time and today I got a new drive shaft AGAIN. There is some still winning from the tranny but the vibration is still there when I drove it home. Something is out of alignment, cracked or not balanced. Any suggestions before I go back to the dealer service guys who are as frustrated as me. I have already written to Ford Canada and was directed back to the dealer.