Posted this on the Barn, but still haven't resolved the issue. Anybody got any ideas? Thanks! http://www.fordbarn.com/forum/showthread.php?t=76788
It sounds to me like you have the wrong turtle for the rear end ratio in your truck. The turtle has to match the rear end ratio. There are 2 numbers on the turtle, divide the smaller number into the larger one and it will give you the rear end ratio. The differential case is marked the same way to indicate the ratio. That's the only thing I can think of that would cause the problem you're having.
Looks like the pictures didn't make it from the barn. My turtle only has one number (19) which I believe crosses to a 3:78. I assumed that was correct for the truck and replaced it with another 19 with good teeth. The fact the teeth were chewed up on the original should have alerted me that something wasn't right. I am going to get some different numbers (18 and 20) to see if that will help. Thanks I'll let you know. BTW do you know where the numbers are stamped on the rear end? I haven't been able to find them. Thanks!!